HL1 (there are also some good Addons like Opposing Force, Blue Shift), HL2 (The main game is brilliant. For what it is, maybe the best FPS till today, E1 is not this good, E2 is better again), DOOM3, Far Cry, System Shock1+2, NOLF1+2, Red Faction, Bioshock and there was one of those Star Trek shooters which had one very nice designed level on a space ship but i can't remember which one it was.
Other well known series like Deus Ex, Unreal, HALO, Star Trek, FEAR, Stalker, Serious Sam and so on weren't so much fun for me to play.
Other well known series like Deus Ex, Unreal, HALO, Star Trek, FEAR, Stalker, Serious Sam and so on weren't so much fun for me to play.