>Barony
A pretty great dungeon crawler, in the vein of Daggerfall or some of the Ultima Underworld games. The combat's really simple, but it does its job (and it doesn't really use dicerolls, so there's that). It's mainly about resource management.
>Ziggurat
Basically "what if we made Doom, but with fantasy elements". It does its job well enough as a simple shooter with randomized elements.
>Slay the Spire
Card game meets dungeon crawler. Can get fairly difficult, but works well for what it is.
>Furi
Shadow of the Colossus meets shmup meets MGR. Also, one of the best vidya OST's of all time. Relatively short, but you'll likely pad the time out with a lot of deaths.
>Star Wars Movie Battles II
Technically a mod for Jedi Academy, but it's one of the best online shooters you'll ever play (and one of the best Star Wars games, too). It's also pretty fucking difficult to learn, but it's absolutely worth it. The community is fairly small, but it's more than 10 fucking years old, so that's to be expected. There's still usually enough people to fill a server or two, though. A good video: https://www.youtube.com/watch?v=hRatNEMQKbE&feature=youtu.be
>Natural Selection 2
A small community, and unfortunately made by SJW cuck devs, but the game itself is pretty solid. It's essentially AVP2 (minus the Predators, sadly), but with some RTS mechanics thrown in. All in all good fun.