Half Life - Playing it through for the first time, just a amazing moment.
Half Life 2 - Having such fun memories of the first one, Valve didn't let me down.
Far Cry - Looked stunning, played well, brilliant fun.
Crysis - Looked brilliant, really enjoyed the game, jumping out of the plane!
World of Warcraft - Amazing achievement, when I was walking down through towards Stormwind for the first time, this feeling of complete amazement, having no idea where I was going, and seeing the city, all the people, and feeling completely lost.
Shogun: Total War - Something a bit different that made me fall in love with the total war games.
Unreal - Amazed me, in the same way Half Life did.
Halo - Playing through that, when I should have being at school on the day the xbox came out, blew me away. Stunning game.