Rimworld

Gotta go with Dwarf Fortress. Been playing on and off for the past 10 years at least, it's just endless !!FUN!!

I really love Supraland, but it’s hard to convince people to try it for some reason.

I really like Isle Wars and Scorched Earth

Just looking though some of my higher playtime games, here's a few I haven't seen mentioned: (I think they're all indie or small studio)

Gunfire Reborn - Roguelike fps with infinite replay.

Troubleshooter Abandoned Children - XCOM style battle system with a really really fun way to customize how your character fight. Story is pretty lame though (I ended up skipping it) and it's pretty grindy.

Thronefall - Pretty challenging base defence.

The last spell - Turn based base defence with lots of different ways to build your characters.

Ratropolis - Roguelike real-time card strategy base defence. Pretty good, although not well balanced at highest difficulties.

Celeste is one of my favorite games period, and it qualifies. The gameplay parallels the story better than any other game I've ever played or seen played, and the soundtrack, art, and characters are amazing. Top tier gameplay and a great story to go with it.

Alternatively, if you're looking for absolutely unhinged strange gameplay made by a programmer rather than a game designer, check out Fractal Block World. It's pretty fascinating!

I haven’t seen it mentioned and feel like it should count, since it really just had a solo programmer working with a graphic designer and musician, but RollerCoaster Tycoon and RollerCoaster Tycoon 2 took a big chunk of my gaming time.

I'll have to go with Selaco, it's not even finished (in fact it's approximately half done) but it feels more complete than any mainline Halo game after H:Reach. Looks better too.

I remember playing an RPG back in the day called “Dink Smallwood” on my old Macintosh laptop, it was one of the few games that were Mac compatible. Really funny and self aware dialogue, pretty great! I found out there’s an app version of it for mobile

Gunpoint. Charming, atmospheric, doesn't outstay its welcome.

Clonk Endevour is not my favorite game, but I played it a lot with friends when I was younger. You can play with 2 or even more people, with just a monitor and a keyboard! Also it's so old it should run on any potato.

edit: real answer is Slay The Spire

edit2: ah shit now all of a sudden all the good indie games I played pop up in my head. Project Kat I enjoyed. Synthetik was awesome. Caves of Qud hasn't been mentioned yet (didn't play it much though).

NaissancE

Clair Obscur: Expedition 33. If that doesn't count. Will....HoloCure or Noita or Parking Garage Rally Circuit.

The Cat Lady and the other games from Harvester Games 👀

hypnospace outlaw

Currently it’s Bellwright, among many other titles. what particularly tickles me about it is the shitty ai voices they used for the npcs. I am not pro ai by any means, but nothing makes me happier than hearing “all in a good days of work.” delivered constantly, in the most off-kilter reading imaginable.

Undertale

Can't believe none of these haven't been mentioned yet: Starsector Kenshi Graveyard keeper Battle brothers Ghost of a tale

Magicraft.

Can't really add much to all of the great games already mentioned. But I'll add one, because it was one of the best games I played in recent memory. Chants of Sennaar. Where to even start? Point-and-click adventure/puzzle game that is all about language puzzles. With great visuals and music. Really dig the eurocomics inspired style. I don't know why, but this game really touched me - maybe it's because the game is about uniting people in an age of discord.

Super Daryl Deluxe

That game has one of the best soundtracks I've ever heard in a game.

Sticking only to ones I haven't seen mentioned:

• Tandis : geometry puzzler
• Gateways : a 2d portal-style puzzler
• Elliot Quest : pixel adventure
• Phoenotopia Awakening : also a pixel adventure, had trouble with the final boss but the rest is great
• Wuppo : flash-animation-style comedy adventure
• Alba : sweet game about a girl who loves wildlife
• Salt and Sanctuary : 2d soulslike
• Legend of Grimrock : tile-based first person dungeon crawler ("dungeon master" spiritual successor)
• A Short Hike (really short but amazing exploration game)

Ones I have seen mentioned but can't bear not to mention:

• TIS-100 : the finest of the Zachlikes; a programming puzzle game
• Crosscode : 2d adventure with incredibly fine-tuned combat and puzzles
• Outer Wilds : fantastic time-loop puzzle
• FTL : space adventure "one more run!" game
• Slay the Spire : deck-drafting "one more run!" game

I suppose I've plugged it recently, but Another Crab's Treasure.

It opens pretty plainly as an ocean-based Soulslike parody with a simple story premise and some self-subverting humor in the dialog with other crabs. As you go on though, every 20th conversation becomes really pointed and real-world-connecting, going beyond just "pollution bad". It's not quite Spec Ops: The Line, but it at least has something to say about society.

The combat is frustrating but addictive, much like Souls games - and it's okay with handing off a number of allowances like accessibility modes and tip systems. It's even helpful that, if I die to a glitch or something bogus, I can actually just choose to re-obtain my microplastics (souls) through a menu.

Minecraft (the old one)