The Kingdom of Loathing it’s funny, it’s free by you get great stuff when you donate, the writing is great and it’s balanced as hell.

Thief the Dark Project, because I like it even though it’s old.

Bioshock, because it’s the best “game as art” example out there

Gary’s Mod for shitposting

And even though I’m not that into Minecraft, I’ll pick that one because you can make video games on it with Redstone so pretty sure that’s a loophole to make Doom or whatever