I LOVE the fallout series. One of the best game lines ever, if I had to pick 3, it'd be the fallout series, the x-com series (retro but has been modded to hell and back, by some folk best described as fanatics, willing to rebuild the source from in-memory code digs, in ASM, with the exception of enforcer, which has the feel of one of those arcade shooter crapfests, and to a degree, interceptor, great series, first two date from the early '90s, but endlessly replayable, especially with the fan hacks and mods.)
And of course, doom. Loved doom III, the overhaul of the graphics really got the atmosphere right.