Undertale. I was blown away by the soundtrack and the cleverness of it all. The twist was good too, but I hated the total completion grind a bit. But it is optional.

Crypt of the Necrodancer. Again, blown away by the soundtrack and how confidently it pulled off the idea of a rogue-like rhythm game.

Insurgency: Sandstorm. This might be stretching the concept of "indie" a bit, but its predecessor was definitely an indie game. This is an excellent arcade/realistic FPS shooter.

Battle Brothers: Battle Brothers is a turn based tactical RPG which has you leading a mercenary company in a gritty, low-power, medieval fantasy world. You decide where to go, whom to hire or to fight, what contracts to take and how to train and equip your men in a procedurally generated open world campaign. The Godfather of Squad-Management-Games!

Songs of Conquest: If you like Turn-Based-Strategy and know HoMM3, you will love this game! Songs of Conquest is a turn-based strategy game inspired by 90s classics. Lead powerful magicians called Wielders and venture to lands unknown. Wage battle against armies that dare oppose you and hunt for powerful artifacts.

OMORI is incredible. The gameplay is okay (typical JRPG stuff), the music is okay (I've heard better in other games), but the storytelling is some of the best in all of video games, up there with Silent Hill 2 and 3.

The Binding of Isaac is an incredibly addicting game. It's basically rougelike 2D Zelda dungeons, and upgrades stack on top of each other. It's the game that I have the most hours in on Steam (specifically the much better-programmed remake, Rebirth). The DLC is great as well, adding a ton of content. Its replayability is damn near unmatched.

Super Meat Boy is just a really fun, fast paced 2D platformer, that is challenging, but fair. The controls are some of the best of any 2D platformer out there, beating out both Super Mario World and Yoshi's Island IMO.

Fight N Rage was my favorite beat'em up before Streets of Rage 4 released, made by mexicans I think, very stylish and manga influenced, tons of juggling and branching paths.

Valdis Story was the hollow knight of it's generation, awesome metroidvania with great bosses and combat with good combos, but it didn't get tiresome like castlevania mirror of fate because regular enemies weren't health sponges, bosses were where you let loose.

Rain World and Space Station 13

Rodina is a very cool space game. You fly a starship - which you can completely design and walk around inside - around an open solar system. You land on planets and asteroids ( seamlessly in real-time) and collect pieces of the very awesome scifi novel-like story. I believe there are now enemy alien bases you enter, but when I played the real draw was the incredible lonely atmosphere of space. It has some of the best newtonian space flight/combat I've played to this day, and the gun play is kind of like old school Doom. I'm sure it's come quite far since I played years ago, but it was literally a one man project at the time.

Graphically, it's very low-poly, and it's not the most varied game, but what's there is 👌

Anyone who likes space scifi should play it. It's incredible, and it came before No Man's Sky released.

Salt and Sanctuary and Hollow Knight.

IDK if this counts, but I loved SPACEPLAN.

Orwell, the first one

Fall Guys, back before the vaulting fiasco