Better speak in terms of genres, huh?
Space Flight Simulator:
Although I have been drawn into the genre by the mighty of
Wing Commander 2, and have enjoyed immensely all the Star Wars games (but Tie Fighter particularly), I have to crown the outstandoing
Freespace 2 from Volition, which took the place of good old WC2 when I thought it was impossible. Best game ever IMHO.
3D Shooter:
Doom II. I have loved things such as "Wolfenstein II - Spear of Destiny" (you guys remember this oooooooooold one?), and newer graphics are great (Doom3 being virtually flawless), but I gotta say - never had so much fun in the genre as I had with that classic.
Strategy Game:
Civilization II. Was there even a contestant? Hope that IV takes the spot.
Adventure:
Those gamers who have been around for a while will certainly recall the swashbucking fun of
The Secret of Monkey Island II, where, commanding the not-so-heroic caracther of the mighty pirate-wannabe Guybrush Threepwood, you face the horredous villany of the Ghost-pirate LeChuck for the hand of beautiful governor of Meleé, Elaine. Oh, and what's that behind you? A three-headed monkey... ?
(there is this new Atari Game, Indigo Prophecy, that sounds like fun. I can't wait to secure a copy)
I guess I should honor the classic
Tetris in this little list. I don't really want to find out how many hours of my life I have wasted placing those little blocks in order...
Regards

.