Following Alvino's setup, no real order.. just games that made me go "Wow.."
These aren't what I consider the best, but rather.. games I thoroughly enjoyed to some degree.
DOOM I & II (PC)
Quake I, II, and IV (PC)
MechWarrior II: 31st Century Combat (PC)
Super Mario Bros. (NES)
The Legend of Zelda: Ocarina of Time (N64)
Halo: Combat Evolved (Xbox & PC)
GoldenEye 007 (N64)
Perfect Dark (N64)
Sonic the Hedgehog 2 (Genesis)
Super Mario Bros. 3 (NES/SNES/GBA)
Super Mario 64 (N64)
Final Fantasy VII, VIII, and IX (PlayStation)
Legend of Dragoon (Playstation)
Sonic Adventure (Dreamcast)
Diablo (PC)
Diablo II + Lord of Destruction (PC)
Unreal Tournament 99/2004 (PC)
Half-Life (PC)
Half-Life 2 + Episode One (PC)
Counter-Strike in general (PC)
Starcraft + Brood War (PC)
Warcraft I & II + expansion (PC)