Stardew Valley: Very relaxing farming game with light RPG elements (i.e. you can build up relationships with people, and can even build up to having a wife [if playing male] or husband [if playing female]). I have more hours into it than I'm willing to admit. Even if you "die" while exploring the caves, or pass out from not making it to bed on time, the penalty for that is rather light. There are also apparently a lot of mods you can add to the base game, but I leave it up to you if you want to start your first run vanilla or not. Controller recommended.

Sub Level Zero: Part of the 6-degrees-of-freedom genre (a la Forsaken and Descent), it combines rogue-lite elements to make for an interesting and replayable game. It has VR support if you are that type of guy, but your mileage may vary as I don't have a headset of my own to test it with. Works equally well with controller and KB+M.

Sky Rogue: A rather simple combat flight simulator with procedurally generated islands. Controller recommended.

Terraria: 2D platformer with light RPG and builder mechanics. It has been in active development (off and on) for more than 10 years since it's original release, and frankly, very few games have a developer that cares THAT much about their game. Controller supported, but KB+M recommended.

Starbound: Basically Terraria, but Sci-Fi.

Knights of Pen and Paper: A 2D-looking game that tries to simulate a Dungeons & Dragon session (albeit dumbed down). I tried it, but it wasn't my cup of tea, but maybe you'll get more out of it. Also has a Sci-Fi themed spinoff called Galaxy of Pen and Paper.

Supreme Commander: Forged Alliance: RTS game that is a spiritual successor to the 1996 game Total Annihilation (which also has mods). Only 2 resources to manage, but you can build an army that numbers into the hundreds, if not thousands. Main goal is rather simple, when the Commander unit dies, the player is out. Best played with Forged Alliance Forever.

AI War II: Real-Time Strategy game with a twist. Whereas most RTS games are PvP, this is a more asymmetrical PvE, where the computer player learns and changes its behavior depending on how you act. There is also multiplayer available if you want to play with friends, more info here. Just a warning, though, it has DLC.

Risk of Rain 2: Having played the first game, and seen my brother play this one, I would choose this over the first one. FPS with roguelike mechanics.

20XX: Spiritual successor to the classic Mega Man games. Controller Recommended for obvious reasons.

Freedom Planet: Classic Sonic spiritual successor with added combat mechanics. Controller Recommended, and try to get it working with a CRT or scanline filter in ReShade if you can. There is also a sequel.

Kerbal Space Program: Literally rocket science! Avoid KSP2, and try to get some mods for the game.

RedOut: Zero-G high speed racing game, more similar to WipeOut series than F-Zero. Supports both controller and KB+M, but the controls will take some getting used to either way.

BroForce: Fast-paced 2D action platformer, where you get to play as 80s actions heroes (with the names changed around for trademark reasons, I assume), going around blowing #%&@ up because 'Murica. It also has been in off and on development for a while. Controller recommended.

Doom (1993): Yes, I'm being that guy, I will gladly admit to being a sucker for so called "boomer shooters". The recent Unity ports make it so you don't have to tinker around with a source port (such as Odamex, Zandronum, or GZdoom), while still leaving the option open for you to do so. Doom I, II, and 64 are frequently available for cheap, with full controller support (assuming you use the Unity versions). That said, if you don't want to support Bethesda (understandably so), there are... ahem… other ways.

Although there are lots more, these are the ones off the top of my head.