How about we break it down into categories instead...
Real Time Strategy:
Homeworld, followed by a distant second, Herzog Zwei
First Person Shooter:
Half Life, then Call of Duty and the Medal of Honor Series
Racing Game:
Gran Turismo 3, and Initial D (Both are really fun)
Real Time Tactical Strategy:
The Commandos series, Desperados, & Robin Hood (All the Same)
Role Playing Game:
Phantasy Star Series
Flight Simulator:
Falcon 4.0, followed by Xwing Alliance
Best Beer Game:
Worms World Party (Take a drink every time a worm dies)

You Don't Know Jack is a good drinking game too.
Fighting Game:
Virtua Fighter 4
Best On-Line Game:
Counter-Strike, then BF1942
My system specs:
Athlon 2800+ clocked at 2.24
9800 Pro with the core at 428.14 and memory at 327.86
1 GB PC3200 RAM
And a PS2 for the console games
My favorite category is real-time strategy or tactical strategy... They require more planning and thinking through a problem, which make them even more enjoyable when you reach your goal.