I'm a Total Annihilation crack whore, so getting hooked on Planetary Annihilation was a very, very short trip. It runs native on Linux. You can build planet killing lasers and put engines on moons to throw them at people. It is most tranquil. Try Frontier First Encounters if you want an open world. It has a procedurally generated Milky Way to explore. Space Trucking FTW. I tried the new Elite Dangerous game from the same authors, but it's a bit shit. Very pretty, but shit. It's definitely a game that does not benefit from multi-player. Diablo 2, Fallout 1 & 2 are regular amusements. Dosbox is quite happy to play them. Spelunky is a fairly kickass roguelike platformer. Hollow Knight is a fun Castlevania-esque game. Both run via Steam. I like Borderlands, but I'm a bit tired of the FPS genre... Style over content for the most part. I've just started into Civ V. I'm not sure I'm cut out for international diplomacy, so I'm larping "Military Industrial Complex Foreign Policy" and just kicking the snot out of people. I may have a VM with a private WoW server (Burning Crusade) on it. It's hard to enjoy MMOs when you hate everyone.