1. Super Breakout - On the Atari 5200 ( one of the first games I ever played )
2. Metal Gear Solid - The 'original' on playstation 1
3.Lord of The Rings Online - Do MMO's count?
Notable mentions: Deus Ex, Half Life/Portal/Counter Strike, Elder Scrolls: Morrowind & Oblivion, Tetris, Shadow of The Colossus, Assassin's Creed 1&2, BFBC2 and of course Crysis