Shadows of doubt is a sandbox detective game. You are a detective and you have to solve crimes, which are totally randomized. What makes this interesting is that the world does not stop:

• the NPCs actually have daily routines
• the murderer might not stop killing
• you can talk with anyone
• and so much more

It is truly a sandbox! I havent played it too much yet, but i feel if i really start playing it, then i will skip going to bed!

Gunpoint. Story based detective game where you solve a murder. Gameplay mechanics make you feel like a badass. You can pretty much finish it in a single sitting but its great.

Heat signature. A stealth based top down bounty hunter game with roguelike elements. Really well done. Made by the same guy that made Gunpoint.

Neo scavenger. A murder hobo roguelike with a surprisingly long storyline.

Super house of dead ninjas. Great fast paced platformer where you’re a badass ninja. Great to pick up and play in short bursts.

Fez. 2D exploration platformer with to change the perspective. Pretty chill and has a cool art style

More well known games that I’ll list anyway in case someones looking for some awesome ones:

Super meat boy

Project zomboid

FTL

Celeste

Crypt of the necrodancer

Enter the gungeon

Spelunky

Noita. Saw it mentionned in this thread and I am seconding this. Great game. But brutal as fuck.

Cave story. A classic. And it’s free.

Owlboy. Took the developer like 10-15 years to make. I’ve heard good things but I’m only just starting to play it.

Also pro tip: if you want more recommendations go look at what speedrunners are playing. People that spend that much time playing a single game over and over generally choose very good games to play.

Signalis

Antichamber

Cave Story

The Beginner’s Guide

Uplink

Hypnospace Outlaw

Exit Fate

The Red Strings Club

Oolite

LocoRoco (not an indie gem but forgotten)

Unciv for Android. It's basically Civilization 5, but FOSS.

Shoutout to Iji, too. Amazing soundtrack and lots of replayability. It's an old game by now, but it's also free. Sidescrolling platformer, killing is optional.

Assault Android Cactus. Dunno how well known the game is, but it's one of the best twin stick shooters/bullet hell I've played, with the android girls full of charm.

• To The Moon: Absolutely heart breaking.
• Tales of Maj'Eyal: An incredible rogue-like with 30+ classes and God knows how many achievements.
• Cataclysm Dark Days Ahead: Apocalyptic rogue-like. Zombies, bandits, aliens and Lovecraft shit. Want to raid a dojo? Learn Judo from a book and proceed to race around town on a pair of rollerblades practicing on the undead? Feel free.

It’s old enough that I can’t attest to how hidden it was/is, but Superbrothers: Sword and Sworcery is likely the greatest 3 hours I’ve spent in a single videogame. It’s chock-full of confidence and style and atmosphere. The story is nothing unique but the presentation is everything. Pixellated graphics contrasted with vivid sound design and a glorious soundtrack. I love everything about it.

Antichamber is hidden gem or simply forgotten? I don't know how much attention it got in its time.
It's a puzzle platformer but I was feeling my brain bend the whole game. And at the same time I never felt like the new mechanic was explained too little or something was artificially dragged out. Very good design.

IMO it was better than Portals

Shadow of the Forbidden Gods - a strategy game where you play as the ancient cthonic entity waking up because the stars are right. Set in a fantasy world where the forces of good slowly become aware of the coming apocalypse and attempt to forestall your return. You have to get past the janky UI and some dreadful AI art, but the gameplay is unique and satisfying.

Parkitect - an amazing RCT spiritual successor with cute graphics, some new mechanics (covering operational buildings and logistic routes). I have 100+ hours in it with my wife. It's such a chill experience.

Nine Parchments - its a dual stick isometric shooter with wizards and elemental spells from the creators of Trine. Great co-op, unlockable characters/spells and creative mechanics. You can combine elements and the spells affect everyone, so for example a poorly placed healing spell can restore enemies health, or a misplaced fireball can hurt fellow players. Great fun!

Wildermyth - turn-based rpg with multiple characters and bite-sized modular quests and random encounters. The storytelling is simply amazing and each campaign plays out over a certain amount of time. The heroes age, retire, their kids can become adventurers as well. They can fall in love, compete, or based on the player's choices even become other creatures or die heroic deaths which will also change how the story plays out. The art style is really nice and unique. I had many hours of fun with this one.

Dominions (Dominions 6 just came out, but it's an iterative game so try 4 or 5 first)

So it's like civilization and battle simulator had a baby, where armies are managed by the unit and there are simulated battles of thousands.

But all the civs are loosely based on different existing mythologies and there's a crazy complex magic system

Oh, and you get to create a god that you can totally battle with.

If you like civ-like games, it's a really unique and satisfying twist on the genre with an incredible amount of sheer depth.

Phoenotopia: Awakening – an amazing metroidvania-related game. Relatively more popular than the other games I list, but is honestly one of my favorite games of all time.

Vision: Soft Reset – a metroidvania, but you can travel backwards and forwards in time and this really matters for gameplay.

Bombe – Minesweeper, but instead of solving the puzzles manually, you create rules ("if there is a cell with the number N and there are N empty cells around it, mark them all as mines") which the game applies automatically.

SOLAS 128 – a puzzle game where you redirect signals in a huge machine, just a great experience if you like puzzle games.

Citizen Sleeper - From the same publisher as The Pale Beyond, it's another one of those story games that borders on visual novels. It's a game about precarity and personhood set on an anarchic, decaying space station. Gorgeous art, fantastic soundtrack and it's uniquely hopeful. Might be favourite game of the last few years.

Mindustry

Hypnospace Outlaw

Plate up : a rogue like kitchen survival game can also be multiplayer , survive as many days as you can getting more customers but also more kitchen gadgets

Back back hero: rogue like dungeon delve with pack management and new story mode where you rebuild a town .

Both are surprisingly addictive and consume my dreams

Andor's Trail is a foss roguelike with a twist that it's story based, something quite rare in this genre.

Immortal Life is a farming game but with a Wuxia twist where you can use chinese magic to help you do your chores and there's a twin stick combat inside the dungeon. What surprised me was seeing the game selling well on steam, but never seeing a single article about it, strangely common with chinese indies over here.

• Beacon Pines -- a charming mystery story with anthropomorphic animals. Has an interesting take on the visual novel formula by having you unlock new dialogue choices as you progress through the story; that way, you naturally explore different paths the story might take. Night in the Woods and (possibly) OneShot fans might like this one.
• Oolite -- a solid FOSS remake of 1984's Elite. Has a bunch of mods for it; some expand the gameplay quite substantially.
• Orbiter Space Flight Simulator -- imagine a Microsoft Flight Simulator game, but you're going to space instead. Or Kerbal Space Program, but without the rocket building mechanic. That being said, KSP fans (and fans of space in general) should enjoy it.
• Transcendence -- Star Control II meets Rogue. A cult classic in the space sim genre that's been in development since 1995. Space dogfighting, trading, mining, smuggling etc, but also traditional roguelike stuff like unlabeled barrels and containers (= undiscovered potions) and permadeath (optional). Highly moddable, uses XML as the modding language. Has a free version (see link) and a Steam release, which includes the paid expansions.

The Witcher 3 (/s)

Crosscode is one of my favourite games of all time. It's an immensely charming action RPG heavily inspired by the 2D Zelda games. It has some absolutely insane combat and surprisingly challenging puzzles. The story is also very good and really touching at times. The devs spent 7 years making this game and I feel like it never got anywhere near the attention it deserved.

It's just $20 on steam AND it has a free demo, so there's no reason not to check it out!

LBreakout[1] is the best Arkanoid clone, period. There has been many attempts by Taito (or Square Enix by proxy) to reboot the franchise but each of their releases just flopped terribly because they keep removing features that people come back to Arkanoid for (the latest PC release, Eternal Battle, has no level editor). In similar vein is Apotris[2] (whose developer is being hunted by the Tetris Company like a fugitive the last few months) is the greatest iteration of Tetris IMO, and it is open-source and developed by a one-man team.

[1] https://lgames.sourceforge.io/LBreakoutHD/ [2] https://akouzoukos.com/apotris

Blasphemous.

Fantastic metroidvania meets soulslike game. The art style, the lore, the atmosphere, and by God - the music!

The combat is not super great, but it's capable enough for a metroidvania.

I haven't played the second one, I hear it's kinda hit and miss.

Null Gravity Labyrinth for everyone who likes labyrinths

Black Souls 2

Hacknet. You play as a novice hacker who investigates the disappearance of a character by hacking into other people's computers to gather information.

The hacking mechanic is fairly realistic and requires you to use the terminal a lot, so it really makes you feel like a hacker. Pretty short and sweet game, and the soundtrack is pretty good as well

In decreasing popularity (estimated by me):

• Creeper World: A mix of tower defense and rts (with pause function) against a ever expanding goo called creep. The fourth installment is 3D and the next one will be a side-view spinoff.

• Tales of Maj'Eyal: Quite popular among the people who are into traditional roguelikes, but I very very rarely see it mentioned outside that community. It's definitely the (nearly) traditional roguelike I put the most time into thanks to its class/ability system that bridges the gap between roguelike and turn based rpg really well.

• The Captain: Technically not indie as it was published by Tomorrow Corp (of World of Goo/Little Inferno/etc. fame) instead of the devs themselves. A mix between old school point and click game, but as a highly episodic space adventure. You travel from planet to planet on an overarching mission and each planet has its own interactive short story. Some are longer, some are very short and you never quite know what you'll find before you land. All of the short stories have multiple endings depending on how you tackle the moral dilemmas it throws at you.

• Infinity Wars actually released before the rise of Hearthstone and also before the popular Avengers movie of the same name. It is to this day one of my favorite digital TCGs, and I played so many of them. Before I get into the main thing that I love about it, I wanna mention that every single card's base version (colorless) is free, anyone can build any deck for free the moment they pick up the game and be 100% competitive with everyone else. The only thing they monetize is bling. Unlike in most mainstream TCGs both players do their turns at the same time in secret, once they both lock in, their moves play out. This gives way for some insane mindgames and outplays that eclipse those in any other TCG I've played. It is a bit rough around the edges, so it might be more of a "hidden diamond in the rough" than a hidden gem.

• Bombernauts is a really fun party game. To sum it up in one sentence: "Imagine if Bomberman was a platform fighter." If you have friends to play with it, buy it on a sale, crank powerup drops up to the max (they stack, which took us hours to figure out), maybe download a mappack and I'm sure you'll have a blast if the trailer looked any fun to you. There's virtually no chance to play it with strangers through as it is super dead.

• Lastly I wanna give a shoutout to Clonk. Clonk is (or was) a 2D sidescrolling game-series that is visually reminiscent of Lemmings. The gameplay is a sort of mix between Minecraft or Terraria (predating it by many many years) and very very very low-pop RTS. It's a mission based game where you control around 1-3 Clonks (the lemmings) and has full online multiplayer support. The missions can range from "build a base in this active volcano", "take out the enemy team's castle", "win this wizarding duel" to "build a bridge across this canyon". What made it truly unique was the community and community creations though. It was created with the explicit purpose to be customizable and users made many, many different maps and modes. It was to me what Minecraft was to the kids in the generation after me (without all the content creators, of course). Some people made an entire RPG in it. Others made what was essentially Among Us, just to give you an idea. Sadly the spiritual open source successor Open Clonk could never recapture the magic for me, and I guess I'm not alone in that because it pretty much died around 5 years ago. If I could make one game popular overnight, it would be Clonk. It did warm my heart to see that some of the celebrated custom map/mode creators from back then ended up getting into gamedev. One of the games developed by someone I remember from back then is Vintage Story.

Holy fuck I rambled a lot about Clonk and I still feel like I'd have so much more to say but this isn't the most fitting thread for that.

Sebil Engineering has a really fun mechanic I've never seen before. Its like those Hot Wheels tracks you always wanted as a kid but your parents never got you, but even better. I guess its a traffic control game? Anyone have other examples of these?

Levelhead is a fantastic mario-maker esque platformer. The official campaign is a little over 10 hours long and is pretty good but its main draw is its incredible level editor and infinite number of quality levels online. I can't recommend it enough. Sadly it never got as popular as it should have but there's still a massive backlog of online levels to play.

Someone else mentioned Distance and I agree. It's a futuristic racing game with some horror elements. The campaign is short, but there's a great amount of levels in the workshop. The multiplayer modes are also pretty fun if you can grab a few friends (there's split-screen too).

Inkbound is launching from early access soon and while I wouldn't say it's the greatest roguelike out there, it's a lot of fun and very unique. It's essentially a co-op turn based RPG where you and other players play all your turns at the same time. I've played a lot of singleplayer too and the game feels well balanced there.

Voxelgram is Picross 3D for PC. Must-have for people who like nonograms.