Smaller vehicles within bigger vehicles, like lots of the Classic Space sets used to have!

My favourite play function is Castle. Hasn’t been made since 2013 unfortunately :(

I always liked the vine-climbing feature in 8780.

The rocket launching mechanism from 6983, such a great set for play, transporting the rocket to the base with the small vehicle included, then removing the rocket from the vehicle with a magnetic crane, which then can slide along a small track to then place it on the launching mechanism. The rocket is horizontal at this stage, so to get it upright the set includes the geared track piece that was used in a number of town and space sets around that time. Turning a knob on this mechanism causes the rocket launching mechanism to slide and turn upright at the same time, placing the rocket now upright on the launchpad ready to shoot into space! Truly a "hands on" set that gives a ton of play value.

Geared articulation a la Bionicle. Making a character or model move with a slight turn of a knob is simple and magical. Wish they would incorporate it into more mech sets.

@commandervideo said:
"Smaller vehicles within bigger vehicles, like lots of the Classic Space sets used to have!"

Well said! Perhaps a sub theme, I also like the ‘escape pod/ship ’ feature like 70701, 75048 and 9498

I loved deploying the droids in 7662. Still roll them out at least once a month! The wheels on the bottom of that massive vehicle were great too.

Thats a tough one! I have two absolute favorites though: The NES running Mario play feature is absolute brilliance, Ive never seen something so clever. Its easy to work, and quite well designed, it hasnt broken yet! My other favorite, while definitely having an opportunity to be improved upon with a single crank, is the wing lifting function on the UCS Imperial Shuttle. I never get tired of it!

When I was a kid it was definitely the letters; putting them postboxes, collecting the mail, putting into larger mail truck, taking that to the train with its mail car, loading it, driving train around track to airport, unloading it, rinse repeat

Mostly basic play features, so you can combine them into your own story. Look at 60233 donut shop or 60216 Downtown Fire Brigade. They have both elaborated, spectacular play featurs, but the prblem is: they're not versatile; it's always they same action over and over. How long will it be entertaining? Thankfully, these big sets have other features, too.
So it's okay when the basic features are drive/ride/fly, open/close, attach/detach, shoot, break, move/lock, load/unload, swivel etc.
A good change over the last years is that you can remove static features like furniture, machines, computers, gatdgets etc. that are held onto the main model with one or two studs. That kind of modularity invites to play =)

The flick missiles used in many sets are so pathetic. When I first encountered the pirate ship cannons and their relative power and velocity compared to the flick missiles, I was overwhelmed and overjoyed by them.

I really like the Ninjago Fire Temple’s ability to split down the middle, and the Turbo Shredder’s giant mouth that eats the minifigures.

My favourites have to be the moving functions in elves sets! They’re always so perfect

Not sure if its a play feature, but I like it a lot

The Wheel function in the LEGO IDEAS 21317 Steamboat Willie set, the two wheels on the side of the ship rotate and the steam pipes move up and down at the same time when he ship is rolled around, works better on a hard surface of course but it runs smoothly and I've never had an issue with it.

Another one, funny enough in the IDEAS theme too, the LEGO IDEAS 21315 Pop Up Book, when opening the book the scenes pop out so smoothly, my favourite is the Jack and Beanstalk one, I absolutely love how the sky platform opens up with the book, again really smooth and well made.

I really want to answer flick-fire missiles and stud shooters as a joke. (I unironically do like flick-fire missiles; my first experience of them was in the Classic Space spaceship build in 10404. Yes, a Classic Space build in a box o' bricks.)

More seriously, off the top of my head:

Everything in Rock Raiders.

Everything in Adventurers and Orient Expedition (I only owned 5988 and the Mt. Everest and India sets). Of note: all the trapdoors, the boulder trap in 7418, provided you position the flex tubes correctly, the use of a printed tan tile to bar the door in 7417, the collapsing bridge in 7411. Does the board game count?

In Alpha Team, the ability to load and drop mind control orbs in 6776 (and similarly the Star bombs in 70849), as well as cause some destruction to Ogel's base using the twin cannons in 6775. The target that you actually destroy in 6775, on the other hand, wasn't great. The spring action was way too difficult to trigger even though landing shots was easy, and when I did manage it, was too startling. The ability to transform 4743 from the Ice Blade to a helicopter is my favorite of the Mission: Deep Freeze vehicle transformations.

LEGO Sports Soccer and Basketball. Say what you will about the weird arms and spring legs of the latter, but it made playing the game more fun than LEGO basketball had any business being.

The Boxor's walking/punching mechanism. Everything about the Bohrok, for that matter, including the fact that Toa can actually wear Krana.

The ability to use Tahu Nuva's Magma Swords as a lavaboard, not just imaginatively but physically. The ability to mount Takanuva on his Ussanui. Pewku's scuttling mechanism.

LEGO Super Mario in general.

Trains in general.

I'm sure there are many more from decades past that I would've enjoyed had I had the chance to own them.

---

Just looked through my collection, some more honorable mentions:

Does the X-Pod Play-Off board game count? Do the DOTS wearables count?

Breaking Harry out of 4 Privet Drive in 4728. The ability to put both Harry and Ron side by side in the flying Ford Anglia, something that still hasn't been fully replicated since even though LEGO has done it with several other modern 6-wide cars.

Everything in 6254 Rocky Reef, my first ever LEGO set.

2224, my favorite Duplo set.

The use of handles attached to neck brackets to perform tricks with Pepper, Sky and the Brickster henchman in 6738.

Speaking of roller coasters, I only have 31084 and haven't built it yet, but as my first ever IRL roller coaster was also pirate-themed with a shark train (coaster fans will have no trouble guessing which one it is), I'm going to absolutely love just to push the train 'round the circuit, even before I get around to motorizing it.

The ability to install the 3D donut sign and subsequently to send it tumbling in 60233.

Taken from Just2good:
7598 has a truck that shoots out pizza
31031 has a parrot that eats and poops out pieces you feed it
70423 has a portaloo that shoots out brown discs

It's a simple one, but I've always really liked any that made use of the trapdoor pieces, like the one seen prominently in 5938. The use in that set was one I found particularly cool - it was also the first time I encountered that piece, or Lego play functions generally, so I may be biased - where the statue and the spear were attached via a chain piece, and pulling the spear caused the tomb lid to raise, revealing the skeleton inside.

Love the mechanical 'jaw-snapping' functions on sets like 8538, too. Squeeze the technic creature's body, and its neck lunges forward and its jaws open and snap closed. That's a big reason why that's still one of my favourite Bionicle sets to this day, in fact.

The working fire place in this year's 21324 blacksmith workshop blew my mind. As a kid, I loved anything that could be transformed by the bricks with holes and technic pins system (classic space) and the light & sound sets such as 6481 Construction Crew that hypnotized me. Besides that, I always liked the little details such as coffee makers or barrels that told their own little stories.

I do love 6973 from ice planet - The large spaceship that splits into smaller ones and can be rearranged in several different ways. Also in that set the garage door at the back section that when opens automatically raises up the wee scooter into launch position!

A few very general aspects:

* Hidden nooks and spaces that you only discover while building the set.
* Efficient use of inner space (especially in vehicles), so it can actually be used to set up several minifigures. Several UCS sets for example provide less inner space than their cheaper and smaller counterparts. Looking at you, 10212 and 75192 vs 75094 and 75257. (I understand that the larger sets require a completely different technical approach regarding stability and that many buyers are only interested in it as a display model, but for me it takes away a bit of the imaginative empathy).
* Different floor levels in buildings actually being connected by staircases, ladders, elevators,...

My favorite play feature was how https://brickset.com/sets/7749-1/Echo-Base
fell apart whenever you tried to use the play feature.

Actually my fave has to be the pop up book’s pop up function. Especially with the Jack and the Beanstalk interior,

7020: Army of Vikings with Heavy Artillery Wagon)
As a child, I was really amazed by the double rapid fire missiles mechanism

8538: Muaka & Kane-ra, 8548-1: Nui-Jaga and probably the rest of the rahi sets from wave 1 of Bionicles
Each set comes with two rahi (monsters) which have mechanisms to knock off each other's masks - great for playing with a friend

I really like the Alpha Mode (transforming) feature from the Mission Deep Freeze sets. 4743 and 4770 were probably my favorites!

The only set we consistently still “play” with is the roller coaster. Not sure if that counts as a play feature in context to what has been mentioned, but it’s awesome to marvel at still to this day.

I love the conveyor belt for the hydrolator crystals in Neptune Discovery Base, from 1995's Aquazone lineup. The crane would be able to pick up individual crystals from a submarine, then drop them into the conveyor belt. By turning the knob on the back wall, you could either deposit the crystal into one of the trans-neon orange boxes or through the processing center of the lab, finally ending up in a storage pit.

This is the first actual play function I encountered as a kid, and it was the first one that came to mind when I saw the article heading.

The explosion mecanism from the old western sets, 6755 and 6765 :D

@ChromedCat said:
"My favourites have to be the moving functions in elves sets! They’re always so perfect "

Agree that the elves theme had some brilliant sets and play features - I wish that the theme had been minifigure based as I reckon many folks will have slept on it and dismissed the entire theme simply through the dislike of minidolls, or boys assuming its simply a 'girls' theme.

As a kid, I enjoyed the AT-ST's walking function in 8038. I also liked how easy it was to dismantle the snowspeeder in 8089 to give the appearance of battle damage (I pretended it was an X-wing until I got 6212). I had fun removing the cockpit/escape pod on 8096. The bone cage in 4182 and the water wheel in 4183 were great as well. 9442's main play feature is awesome. And I can't forget 76035! I could go on and on, there's so much nostalgia!

The best play feature, though, is definitely the Lego minifigure. The most annoying is the stud shooter.

Out of the listed set I prefer the mine set over the big vehicle. (even while I have neither)

Vehicles that Split are awesome :
70315 : Clay's Rumble Blade - 2 bikes, a Sword-Jet and a spring loaded missile platform
70322 : Axl's Tower Carrier A big 6 wheeler with a tower that can seperate and a big catapult appears

72002 : Twinfector - Splits into 2 hover bikes
72004 : Tech Wizard Showdown - A Minifigure inside a Mech inside a Mech

Helicopter type sets with a wheel that makes things spin :
70353 : The Heligoyle - Rotating the round button on the handle makes the "wings" turn around.
70356 : The Stone Colossus of Ultimate Destruction - button on the back makes big wings flap

Trapdoor into big monster mouth:
70323 : Jestro's Volcano Lair - also had other playfeatures like a prison wall breakout, a destructible wall section when hit, and a sawblade near the entrance stairs.

Airdrop of a Minifig / Mech / Bike :
70361: Macy's Bot Drop Dragon - Minifig Bot Drop as name suggests
72005: Aaron's X-bow - drops bike
72003: Berserker Bomber - drops mech suit.

Vehicles that transform :
70321 : General Magmar's Siege Machine of Doom - Can raise up to form a tower or be a 6 wheeler
70351: Clay's Falcon Fighter Blaster - wings sliding to form a wider shorter craft
70348: Lance's Twin Jouster - Deployable as a flyer
70312: Lance's Mecha Horse - Mech Horse or Chopper Bike modes
70354: Axl's Rumble Maker - not as amazing but still could turn into some sort of flyer or mini tank tracks for a mech-suit, and rotating drills when moving.

Just a bunch of sets I really liked the playfeatures from, and much moreso then the many many shooter functions included.

Many more of the Nexo Knight at least had some play feature , mostly projectile based, some moving parts, or buttons to press.

I love a trap door, especially ones where you pull out a pin and the floor drops away.

Or hidden area, like a revolving bookcase.

Finally I really miss the moulded bases, I think they added good play value, especially rams for vehicle to roll down.

I absolutely love the feature that changes Bruce Wayne into Batman in set 6860 of the Batcave from 2012. It is brilliantly designed. You place him on top next to the Batphone, send him down the lift/platform/elevator to change into his Batsuit. The function is pretty smooth (never got 'stuck' for me) and happens fast. Blink and you miss the trick. You know, it is like a magic trick because one minifig disappears and another takes its place. Set 7783 of the Batcave (from 2006, the original) also has a transformation feature but not a clever one.

I also liked the simple functions in classic space sets a lot as a kid, like the doors at the back of 928 Space Cruiser, where you could lower a ramp to drive down a moon buggy, the hinge at 6890 Cosmic Cruiser that allowed you to release a small space craft from the back, but also simple roll-down doors like in 6382 Fire Station or opening cars or planes like 6367 Semi-Truck or 6368 Jet Airliner.
Those functions gave me hours of joy as a child, even though they were so simple.
Today I like remote controlled functions like in 8043 Motorized Excavator or 42095 Stun-Racer, as I normally don't really play with Lego anymore. I just sometimes go into my daughter's room and go a few rounds on 10261 Roller-Coaster. That's still great fun!

@Apedemak said:
" @ChromedCat said:
"My favourites have to be the moving functions in elves sets! They’re always so perfect "

Agree that the elves theme had some brilliant sets and play features - I wish that the theme had been minifigure based as I reckon many folks will have slept on it and dismissed the entire theme simply through the dislike of minidolls, or boys assuming its simply a 'girls' theme."

For me , it was the Timing of the theme , I didn't collect LEGO from 2001-2015 basicly, and 2016-2018 I strictly only collected Nexo Knights (which also had books/magazines etc) , and also why I listed them as playfeatures here.

By the end of 2018 Elves had almost retired, and I sort of regret it now, but also back then I had no experience with minidolls and at that time was a bit meh about them.

For me, it would be the Shadow Puppet show in 70751 Temple of Airjitzu, the flight transformation in 9446 Destiny's Bounty, and the safe-grabbing in 5971 Gold Heist!

@morvit said:
"My favourite play function is Castle. Hasn’t been made since 2013 unfortunately :("

That’s a theme, not a play function. But I’m guessing you realize that.

7674 V-19-Torrent's wing folding feature is very neat, as all three wings fold up and then it also extends its landing gear.

10195 Republic Dropship with AT-OT: the dropship picks up and drops walkers very effectively, and it also works quite well with 7675.

The hidden weapons and wing configurability of 8943 and 8942 are nice to play with.

6860 The Batcave's transformation feature is great, even though I don't own the set.

It seems today all they do is slap some stud shooters or spring loaded shooters on a model, include a storage box for the extra studs and call it a day. Bit of a generalization, but still.

All the Rahi (8537 8538 8539 8548 & 8549) had great play functions that took the spirit of the more maligned Technic Competition line, and mixed it with an animalistic theme. A giant scorpion fighting a giant bull and both have lever functions that trigger on attack? A robotic crab with RC control? All very impressive, and all very much still in line with Bionicle's early years as a Technic subtheme. As dull as it was that Lego re-released the Bohrok design in TWELVE identical clone sets... I can hardly blame them too, since already mentioned the Bohrok were also incredibly well built for play and function. They roll up into a ball, simple and immediately fun; then can be turned into an action figure via moving a few pieces!

That reminds me... I still need to rewrite my old review of the Manas set someday after I realized how to get the RC functions working right. Its a lot more fun and impressive to have working, and I unfairly dunked on the old set because of construction errors I made as a kid.

I also love just, detailed vignette scenes. That is something I have loved about the modern Hogwarts castle sets. Each one has tons of tiny little rooms that in a few simple pieces of furniture capture a scene. It just, looks good; and I am sure for kids it makes a great dollhouse style play scenario.

The lever on a set like 10257 to turn the Carousel around, or other mechanical functions that "make sense" also always impressed me.

My favourite play functions are transformations and additional vehicles. For example, 8964 Titanium Command Rig can transform from a mobile drilling unit into a mining base without any disassembly required, and 7699 MT-101 Armoured Drilling Unit contains an additional flyer and a bike stored on its chassis; 8635 Mobile Command Center is an excellent example of the latter, with the main truck containing 5 additional vehicles.

Echoing a few people here but I love a good trapdoor in a set. Especially if its the pin-pull kind. Also, anything with some kind of working crane or rope winch mechanism, even if not necessarily used as a crane... Such as the web mechanic on 9470 Shelob Attacks.

Also got to ditto on the 'large vehicles with smaller vehicles'/escape pods and sets with 'revolving bookcases' or other similar hidden space concealed door.

@Lego_Prime said:
"My favourite play functions are transformations and additional vehicles. For example, 8964 Titanium Command Rig can transform from a mobile drilling unit into a mining base without any disassembly required, and 7699 MT-101 Armoured Drilling Unit contains an additional flyer and a bike stored on its chassis; 8635 Mobile Command Center is an excellent example of the latter, with the main truck containing 5 additional vehicles."

Agreed, those features are lovely.

I didn't write in in my first post but while 70352 : Jestro's Headquarters was a pretty weird set, but it did have a quad, a boat both stored inside, and the top of the head is a flying jester hat , and the trailer can seperate, which was basicly the main play of the set beside the Crane/prison cell.

All the functions of the Adventurers sets and Oriënt Expedition sets. The Unitron Monorail and the Futuron Monorail have some really great functions.

Of the sets I owned? 6541, with its two cranes to move cargo from the ship to the truck and back, and each of the crates had their own vehicles inside as well. Amazing set.

Everything on the Death Star. Such a brilliant product. The elevators (two of them!), the closing trash compactor, the way the prison block actually had a chute leading into the trash compactor, the moving superlaser, the moving turbolasers... All so much fun.

The simple ramp mechanism in 6981 Aerial Intruder is one of my favorites.

But I'd give the prize to the entirety of 6989 Mega Core Magnetizer, for such a great-feeling steering mechanism, incredible cockpit, and so much more.

On a related note, most of the retro space sets with cool steering mechanisms were designed by Jørn Thomsen, so you have them to thank!

Though I don’t own it, the crystal sweeper set from power miners has always captivated me. It’s an amazing play feature and looks incredible. The original destiny’s bounty engine feature is also pretty amazing

Power Miners had some great functions; 8961 Crystal Sweeper picked up crystals with spinning harvester blades and 8960 Thunder driller had a contrarotating drill. Also, 7775 Aquabase Invasion had a neat minisub deployment slide

Monorail... and the shooting cannon.

Other play features I've really enjoyed:

- The dynamite explosion function in Wild West sets like Sheriff's Lock-up. I've even made variations of that function to simulate Force Pushing abilities with my Jedi and Sith minifigures. It's so great, not sure why LEGO hasn't integrated it more regularly into sets.

- Multi-stage rubber band pulley systems allowed for some fun in Time Cruisers and Time Twisters themes. When you would roll the Hypno Cruiser (for example) forward, it would cause not just the Hypno disks to spin, but also a propeller on the roof of the car.

- Cyber Slam for Technic in 1998 had some excellent play features not replicated even in BIONICLE. For example, 8245 not had a tricycle with a punching arm activated by turning a knob, but by having it hit the target on the Scorpion robot, a bungee cord would be released, accelerating the robot towards you unless you got away in time! And if you didn't, it was likely the front wheel of the tricycle would hit a bumper on the front of the robot that would activate the release of its claws around you, trapping the vehicle.

- The Bohrok, as mentioned before, were a marvel of compact play features. Not only could they be folded into a ball for easy storage, but in default configuration, pressing a lever on the back would snap the head forward for a devastating gut punch. Additionally, hitting or flicking the neon-colored teeth (or "eyes" to most people) would cause the faceplate to fly open and the brain pan to throw the Krana brain at the attacker.

I was also a fan of pull-away trapdoors, shooting pirate cannons, revolving doors, magnets, and modular construction, but those examples I mentioned, along with the conveyor belt in the Neptune Discovery Lab, were standouts from my childhood. Modern examples of play functions that stand out to me are few and far between, but I was particularly enamored of how LEGO finally got the movement and positioning of the wings on Boba Fett's Slave I right with the UCS version in 2015.

My favourite play functions were always in Castle. There was so much lore to fuel your imagination that even the most basic of features could be made interesting.

Who can forget the glow in the dark ghosts, too? They were amazing!

Lego sports has some of my favorite play features. Mainly basketball and soccer.

8634 was pretty fun as a kid I always raced those two cars and loved to customize them.

60047 Had a ton of good play features making my favorite set of 2014 (that I own)

I loved the play features in 7623

8960 and 8961 were fun to play with

7199 was really fun. I mean REALLY fun

I liked that their is a hidden blaster in 5972

41130 was a set I had fun with

I liked the "Popping" feature in 75169

I liked the play features from 10262

I used to like the play features in 4567 as a small child but now I don't like the set.

It was fun to use 5359

I'm in the Classic Space vehicle within a vehicle camp. Love that feature more than any other.

I was also one of those who liked Classic Space vehicle in vehicle when I was a kid.
But having just built 10273 Haunted House, that has probably the best play features of any set I've ever built. The light brick is clever and the lift is a great mechanism that never ceases to amuse.

In no particular order, my taste in sets actually leans toward multiple features being present in one set over the set's budget just going to make it look prettier. I like everything to be tricked out and multifunctional!

- Hidden storage spaces. Lots of them.
- Hidden rooms and/or entrances
- Hidden traps like those in the adventurers theme. Especially the more creative ones, and especially if there are many in one set
- Vehicles that split into multiple vehicles á la the space themes
- Vehicles carrying smaller vehicles, or 'mothership' vehicles
- Vehicles with enough interior for minifigs to do things while it is moving. (Mobile bases?)
- Vehicles that transform. It's to the point where I find vehicles without this boring sometimes.
- Modularity. Especially if one unit is used over multiple sets. Be they buildings, vehicles, mechs...
- Hinging sides that can change the layout of a building to a wider or enclosed look.
- Geared mechanisms in figures or mechs.
- Kinetic action features. I love the Boxor for the satisfying punching motion you make by wobbling it.
- Does a mech or figure with sensible articulation count? I mean that the arms can actually reach stuff and the legs move more than one click before a stopper prevents you from placing the foot down. A turning waist... etc.

Too many things to count. I love it when sets expand like the Monkie Kid HQ, or when a set can be broken down into small builds and then combined into a large build like the Bone Demon.

I will second the ships in ships and transformation features that everyone has noted as well.

The one that can go away though forever are stud shooters. I don’t recall ever using any variation of stud shooter.

@christopher94 said:
"The one that can go away though forever are stud shooters. I don’t recall ever using any variation of stud shooter. "

Agreed they aren't fun (as an AFOL) , and the small projectiles just can get lost easily (that includes 1x1 tile shooters and minifig crossbows shooting bars or tiles as well).

Flick fire just don't really work very well either.

Also the hard ball shooters are pretty bad too, they go way too fast/uncontrolled. (set 70324 has a target to hit , but still think a rubber tip missile might've been better)]

I hope instead of ball shooters, that LEGO will use more colored versions of missiles seen in sets like 60281 : Fire Rescue Helicopter in trans-light blue, but could be trans-orange or something for fireballs in the future, or even in Brown in a Castle ballista.

Disc launchers, spring loaded missiles (including rubber tip) or catapults aren't as bad.

Drawbridges and winches

Further to my last post, I also really liked the fold-down / open out feature of 8001, too. Not only did it feel very accurate to the movie, it was quite cleverly executed as well. Folding it down was manual, of course; but then with just a press of the button on its chest, its legs unfolded and its head swung up into position. Then a turn of a small gear on its back lifted its right arm up over its shoulder to reach the blaster tucked into its backpack - and a magnet connection between the two meant that turning the gear back made it smoothly pull the blaster into its hand. The fact that its was all integrated so neatly without compromising the droid's appearance in any way just made it all the more fantastic; it was a lot of fun to recreate the "activate the droids" sequence from the movie.

I've heard that 8002's unrolling play feature, from the same wave, is even more impressive, and I'm ready to believe it; but I've not actually seen it in action myself.

The crab/lobster oven in Ninjago City is pretty clever…

Might be a bit of an unpopular opinion, but my fav function is one that involves flick-fire missiles: the machine gun of the republic attack shuttle.

It's just so satisfying to load the magazine and then press the button on the back repetitively and pew pew pew at the droids you lined up against the wall waiting to execute!

Honorable mention: Pooping parrot

Great question, there are so many brilliant play features just picking from sets I own. 6890 little ship in a big ship, I particularly like this style where its the same pilots seat for both vehicles. Fly the ship in orbit, touch down and use the smaller ship on the planet! Similar with 6826, you could park up and then scoot around. I had hours of fun rebuilding the L&S from 6480 into my own vehicles. 6892 gave you double the detachable sections to play with, drop the command centre, drive further on then escape in the ship!
10220 had a lot of cool features and was pretty accurate to the full size camper interior of my own van. Combining 9516 and 75005 one of top of the other is probably peak play function heaven though
Of the more modern sets, the light up forge from 21325 is a really nice addition.

I generally just like things that open and close, whether it's doors, cockpits, hatches, wings, vents, secret compartments, or whatever. The Agents truck was great for this. There were like 10 different things you could open up or fold out on that model.

I bought a used copy of 7317 this year and finally got to experience the aero-tube system (I never got around to the one Mars Mission set that used them most recently). It's a very cleverly engineered system in it's own right and I spent a lot of time messing with the details of how many tube links could carry the pressure, hard push vs soft push, slow push vs long push etc. With the additional ability to change from positive pressure to negative with a simple twist of the pump seals the deal for me to make it my all-time favorite.

@Galaxy12_Import said:
"I bought a used copy of 7317 this year and finally got to experience the aero-tube system (I never got around to the one Mars Mission set that used them most recently). It's a very cleverly engineered system in it's own right and I spent a lot of time messing with the details of how many tube links could carry the pressure, hard push vs soft push, slow push vs long push etc. With the additional ability to change from positive pressure to negative with a simple twist of the pump seals the deal for me to make it my all-time favorite."

Definitely agree with you on this one, basically came here to say the same thing. Special mention goes to the glow-in-the-dark hypersled included in the set, which glows so brightly that you can see it zoom through the tubes, lighting its path along the way! Life On Mars was such a great theme, and this set happens to be my favorite set of all time, due in part to the incredible play feature. I made a point to collect every single set a few years ago and I'm so glad I did!

The separation of front and back of 6931; the walking legs of 6940; the interchangeability of Blacktron modules; the functioning control stick of 8855 and spiritual successor 10226; the fold-out wings of 6886; the magnets of M:Tron (whatever happened to magnets in Lego anyway?); the brilliant (though temperamental) design of 8002; and finally 21309, which is about as close to perfection as any set has ever gotten in terms of play features. Oh, and the TV from 71374.

Most of those play features still hold up today, but these are all from the perspective of my experience with them as a kid (and kid at heart...).

@DragonLord56 said:
"For me, it would be the Shadow Puppet show in 70751 Temple of Airjitzu, the flight transformation in 9446 Destiny's Bounty, and the safe-grabbing in 5971 Gold Heist!"

That shadow puppet show is perfection (except how easily the wall falls off). I have made up so many stories for those two trophy figures to tell my kids, and they just sit enraptured. Too bad there's always the wall of flames between them, and then that snake!

Spaceships that split apart
Castles with secret doors
Walkers 6940, 6876 , & 6878
Cannons that shoot

Don't know if they count as "play features" but I like complex but visible Technic mechanisms and sets that have several Technic functions in one model. Something like 8880 supercar.

I love the cleverly hidden winch in 7189 Mill Village Raid, but confess that the novelty of a water-wheel-driven blacksmith's hammer has rather worn off. Blacksmiths in general are common as muck, in fact. I think I have five (!) in my little medieval village. Six if you count 6041 Armour Shop.

I want to add, this is a fantastic idea for an article--I'm having a blast going through all the comments (yay hover-over model numbers!) and discovering tons of sets I've never read about. This article and the comments are at the heart of why we all love Lego, so thanks!

I've read every comment so far and looked at all the the sets linked to and, wow, LEGO is bloody GREAT!

The whole Nexo Knights theme has completely escaped my collection, but the more I see of it the more I like what I see. I would have loved it as a kid for sure.

I'll start with agreeing wholeheartedly with lots of the suggestions so far.

@Everyone - Deployable mini-vehicles, especially in Classic Space, like in 497 and 6931 .
@Mr__Thrawn - 2507 Ninjago Fire Temple - entire two storey building splitting right down the middle revealing a huge dragon
@Pekingduckman - 70423 Hidden Side Paranormal Intercept Bus 3000 - Portaloo gets possessed, flips out and shoots poo discs from it's toothy maw
@SolidState - Geared articulation a la Bionicle (though I'm more familiar with Slizer / ThrowBots, 8506 has an awesome chopping action for it's dual pick axes)
@DragonLord56 - 70751 Temple of Airjitzu - Rotating, illuminated puppet show theatre

Similar to the functions in @CapnRex101 's nomination 7036 Dwarves Mine is one of my very earliest LEGO-building memories, 360 Gravel Works. 1x1 bricks transported around the site using a crane on rails with a winch and a spring-loaded grabber, working tipper truck and scoop digger side-vehicles, and a working conveyor belt system. LOVED it.

The fold-out playset function in Classic Castle 375 was so great for really getting full access to all the interior sections of an otherwise fully four-sided castle. I'm sure this type of functionality has featured in tons of big sets over the years, but in the modern era 80013 Monkie Kid's Team Secret HQ (Sea Crate HQ) is a premium example of a fold-out playset. Have a look at a video if you've not see it closed and opened, it's perfect.

I like mechs with spinning weapons too for playability, and there are loads to chose from in the Ninjago world. My favourite might be 70725 Nindroid MechDragon. Twin wing-mounted serrated discs spinning at crazy RPMs with a really clever mechanism.

Air storage tanks for Technic Pneumatics were great fun, and really boosted the existing pneumatic functions, as in 8462 Tow Truck.

Simple pull-back motors like those in the 8354 to 8371 Racers range and the especially in the almost annual Technic offerings of paired vehicles. Available separately, but with instructions for combining together into larger, much more powerful ones ( 42046 and 42047 are the best IMO).

Ninjago nailed it again with a working lobster oven in 70620 Ninjago City.

I love love love small, working versions of real-world vending machines, like ATMs, arcade games and drinks dispensers. My favourite is the smart phone-operated mystery gift dispenser in 80020 White Dragon Horse Jet set from the Monkie Kid theme. Such a cool mechanism, and the amazing graphical style and build quality really add to the appeal.

@ra226
"I want to add, this is a fantastic idea for an article--I'm having a blast going through all the comments (yay hover-over model numbers!) and discovering tons of sets I've never read about. This article and the comments are at the heart of why we all love Lego, so thanks!"

I TOTALLY agree! -Well said! :)

Can’t believe no one has mentioned the simulated hydraulics of 6927 All-Terrain Vehicle! As you open/close the vehicle’s locking arms, the building being transported is gently lowered/raised into position as if it were using hydraulics. Simple but brilliant! If you’re not familiar with this play feature, check out JANG’s review: https://m.youtube.com/watch?v=-ofo_BScIpo

I’ll also second (third? fourth?) @commandervideo’s nomination of vehicles-within-vehicles.

75005, the Rancor could actually eat minifigs. And 8633, the sharks could actually eat minifigs...and had friggen lasers on their heads. And 10178, the AT-AT can actually walk (rumors that it can actually eat minifigs have yet to be proven true).

Worst play feature is a toss-up between my first Pirates cannon, which was a spring-fire design (after they stopped installing springs in them for safety reasons), and the minidoll.

@LegoSonicBoy:
My 6-wide Ford Anglia MOC has both Harry and Ron in the front seat, with Harry’s trunk, Hedwig, and Scabbers in the back, all in a car that’s the same size as the official versions.

@Lego_Lord_Mayorca:
Definitely eyes. The white bits on the original Bohrok, and silver ones on the Bohrok Kal, were the teeth. Artwork also shows the eyes glowing before they appear out of the darkness, which is a common trope with pretty much all Bionicle villains.

@ThatBionicleGuy:
If you built it right, the Droideka did transform as advertised. The problem was it required a ton of tension on the trigger, which meant using a pile of black rubber bands. I don’t know if the Technic band would work, but the black ones from that era would rot away really fast. There was also 8000, which unfolded when you punched its eye (just like in the movie).

@ra226:
What happened to magnets? Kids getting perforated bowels. No, seriously, look up Buckyballs. I don’t know that LEGO magnets were ever cited in an emergency room visit (accurately or not), but following one manufacturer getting raked over the coals, others tend to adapt their product offerings to avoid a similar situation, like when Lucasfilm made Kenner scrap their rocket-firing Boba Fett action figure in favor of one where the missile was glued in place, all following a lawsuit that was erroneously filed against them when a kid choked on the missile from a Cylon Raider toy.

The whole Hidden Side theme has awesome transformation features as vehicles, buildings and settings become demonically possessed. 70425 Newbury Haunted High School has probably the most dramatic and extensive spooky transformations.

The best transformation set IMO, packed with unfolding OMG-level features (assuming the overall aesthetic doesn't make you puke rainbows), is 70828 Pop-Up Party Bus from The LEGO Movie 2. Going from sleek space-transport to insane dance party including a rotating, glitter-ball-illuminated dancefloor in just a few simple and very reliable moves. Such a clever design.

Shout-out to all the jail-break / safe-stealing sets! What's better than a tow-truck dragging a bank vault down the high street as sparks fly and green bills and gold bars fly about the place? 60140 Bulldozer Break-In is our favourite City playset.

Nobody choosing Vidiyo's online functions as their favourite? ;)

My LEAST favourite function is all of Powered Up features of poor old Batman's 76112 App-Controlled Batmobile. I bought it new, discounted to around 30% of the RRP (70% off) and STILL felt cheated...

Oh, another one I liked is from the Galaxy Squad theme, 70708: Hive Crawler.

My son initially got it as a gift, but I had to get my own because the leg motion, as one drags it along the floor, seemed so realistic. While in motion, its rattling sound, coupled with the seemingly random choppy up-and-down leg motion, greatly unnerved our cats to the point of frightening them away! :-)

Anything mechanical! Gears, chain-links, slidey-moving bits... I love that moment in the construction process where you can start turning something or pushing something to see the internal workings go, even before you've finished the build.

@PurpleDave said:
" @Brickodillo:
Dimensions is fun, but insanely expensive at MSRP. If I was younger, I might have said the “clinger” brain slugs from Alien Conquest (which might explain why I have over 200)."
You sure you aren’t hijacked by a brain slug (buying over 200)?

Going along with the "ship inside of a ship" idea, the Spyrius space sets had some great functions like that! I loved how you could swoop down with 6939 to drop off the rover with the android, and the way the 6949 Robo-Guardian's arms could lock in position and and could also be attached to the "head" then fly the head around... (I could go on for a bit with that set!)

Space Police 2's 6897 also had a great function to drop or pick up the prisoner cell.

Anything where I can turn a knob to make something happen: The S-foils on most X-Wings (particularly the "snappy" action from 2012 onwards), extending the droid rack on 7662, or adjusting the engine pods on 70815.

Love a good bomb drop mechanism, 75172 is a prime example. It's very simple, and if you fiddle with it a little, you can get all four bombs in there.

The hidden weapons in 70802 are super neat.

4743 's transformation function is really cool, and I think the standout from the whole theme.

The titular vehicle from 7626: It has the smoothest-running tracks I've ever seen in a Lego set, an absolute joy.
The way the blades are powered is simple but very effective (they each rest on a rubber-tyred wheel that runs on the ground). And even the "exploding" feature works pretty well.

Everything in 10188, but particularly the TWO elevators and the sliding door.

The Saturn V being able to seamlessly seperate is just... [Chef's kiss]

My favourite play feature is a train

In terms of reconfigurability, Classic Space's 6952 is one of the best (look at the back page of the instructions for the options)! Turning the wheels into hover pads may not make much sense but it is always a bit mind-expanding to see parts used for something other than their 'intended' purposes. 6951 also would have been awesome to play with as a child with its multiple attaching components.

The modularity of the Blacktron I sets could have been an amazing play feature had it been executed slightly less haphazardly (as it is, intra-set modularity is great but inter-set modularity is lacking (at least to my adult eyes)).

I love the ability to basically recreate the entire Apollo 11 mission from launch to splashdown in 21309. The stagings of the Saturn V are always fun to demonstrate as I explain the mission sequence to others.

On a slightly related note, I think the alternate models that used to be shown on the backs of boxes were an excellent play feature as they encouraged alternate building and sometimes demonstrated creative uses of pieces. While some of these alternate models could be a bit goofy (especially for tiny sets with a limited number of pieces), some of the better alternate models were arguably better than the sets themselves. I am sure many creators of MOCs honed their skills trying to reconstruct some of these alternate models from an image seen from a single angle!

I've wanted 7036 Dwarves Mine (from the thumbnail) since I was 8 and just managed to get it this year. Slide functions like the gold in it are always lots of fun to mess with.

The BIONICLE fan in my absolutely adores articulation, so stuff like Exo-Force Mechs, Ninjago Dragons, Mixels - you know, anything posable - are always awesome!

On the topic of BIONICLE, the Bohrok of course. They might just be the best "playable" LEGO product they've ever put out. Pressing a lever on their back would make them thrust their heads forward as a headbut, flicking their eyes would cause them to launch their Krana at an opponent, and their limbs could be curled up to turn them into a compact ball. The great play features even extended to their packaging, the lid had a indent in the top that they could sit in while in ball form, and the set came with this weird pin+clamp that could let them hang suspended inside the packaging (which was clear, making it look like they were in their "eggs/hive")

8595 Takua and Pewku is amazing. I only got it like 2 or 3 years ago but she's got this awesome scuttle function as you slide her across the floor. My model is missing a part or two of the guttyworks, but even so it works like a charm and is simply mesmerizing.

8556 Boxor was awesome. Pushing/leaning it on it's feet would cause one of it's fists to swing forward and punch whoever's in front of it. I used to make it "dance" a lot.

I've got to give a shoutout to combiner models. They were ridiculously common in BIONICLE, Mixels, and Power Miners and I think its a shame other LEGO themes haven't picked them up much. In fact, the last example I can think of that wasn't a character was Port Royal (or was that the original set???) from Pirates of the Caribbean.

Okay one last BIONICLE one, the Visorak Minifigures from 2005 and the HERO Factory Jumpers from 2014. They were little rubber spiders where you could push down on their butts to make them jump forward. That appears in a lot of toys, but you don't see it in LEGO often and it's fun to watch the lil guys fly!

Of course anything modular is awesome. As many have said before I adore spaceships with a bunch of reconfigurable components, bonus points if you can mix and match sets from across the line!

Orient Expedition and Ninjago Master of the Mountain both had a function of combining all the sets in the wave to create a giant board-game. Playing a regular board game can get boring 'cause of how flat everything is, and playing an online one can get boring 'cause it's not as tactile, but with LEGO you get so much depth and complexity with a board that is massively customizable.

2507 Fire Temple was my first $100+ set. I loved the function of splitting the temple open, and when my grandpa gave my brother and me a vile of genuine gold we hid it underneath the temple as a secret treasure.

A smaller thing but I had 6239 Cannon Battle as a kid and the ability to blow apart the wall was just so addictive. When I first discovered LDD I recreated that function in... well more builds that really needed it.

I never owned 8961 Crystal Sweeper but I always thought it's ability to sweep up the crystals and then move them *up* into a bucket was awesome, not to mention the sheer amount of crystals it came with.

My only trains were the latest Harry Potter one and the Hidden Side one, but I've always wanted to get a decent amount of rails and automatic wheels to set up a proper track. It would be so cool!

Someone else mentioned 10195 Republic Dropship with AT-OT Walker. I've never owned it but I'll second it's compatibility with 7675 is so epic!!!

Waterwheels are always cool, especially in blacksmiths.

I actually unironically love the modern 1x4 spring shooters, as long as they're well integrated into the build with triggers instead of just being slapped on top. Even when they are just slapped on top I sometimes like them ... the six-shooter X-wing, with a spring shooter on every wing and stud shooters where the proton torpedoes would be, is awesome for play, even if it doesn't look so great. I'm so glad that starfighters and similar vehicles come standard with a pair of spring shooters now ... it means that even the smallest starfighter can actually do something now (shoot at stuff) instead of being a simple rigid body for swooshing.

So yeah. I must be the only AFOL who comments on Brickset to actually love the spring shooters and stud shooters. They add so much playability at such low cost, which is why they're in so many sets.

@PurpleDave said:
"(...) the “clinger” brain slugs from Alien Conquest (which might explain why I have over 200)."
Ol' reliable strikes again! This fella CANNOT resist an opportunity to talk about his massive clinger collection.

Though, on the subject of Alien Conquest, the simple-but-satisfyingly-effective abduction feature of 7052 is always entertaining!

@bananaworld said:
" Though, on the subject of Alien Conquest, the simple-but-satisfyingly-effective abduction feature of 7052 is always entertaining! "
Oh, yes, and another brilliant use of a light brick. The soft-tipped spikes on the underside of the 7052 UFO project a red targeting cross-hairs down over your unwitting rural minifigure victim, then you lower the craft over him, lift off, and he's gone! That's got to be the best play-feature of all.