Quake, which introduced me (and millions more) to the wonderful world of online FPS deathmatches.
Unreal Tournament, for continuing that tradition.
Half-Life, for being an awesome game which revolutionized FPS games.
Fallout 2, for being amazing.
Diablo, for wasting more of my time than possibly any other game, up to and including Diablo 2.
Deus Ex, for being amazing.
Thief (and Thief 2, which came out in 2000), for being awesome and starting the 'first-person sneaker' genre.
System Shock 2, for a great storyline and being really damn creepy.
Total Annihilation, for being one of the best RTS games, ever.
Sid Meyer's Alpha Centauri/Alien Crossfire, for being one of the best TBS games, ever. I still play it to this day, and enjoy it more than any of the Civilization games.
Nethack, for being as old as I am and still truckin' (not that I'm that old, but for computer games, Nethack is).
