Shooters:
BioShock
CoD4
Gears of War
Gears of War 2
Resistance 2
Halo 3
Racing:
Paradise
Forza series
Gran Turismo 5 Prologue (and the full one too when it comes out :D)
Mario Kart Wii
RPG:
Fallout 3
Oblivion
Valkyria Chronicles
*insert JRPGs here*
Action / Adventure:
Uncharted: Drake's Fortune
Metal Gear Solid 4: Guns of The Patriots
Ratchet and Clank Future: Tools of Destruction
Others:
LittleBigPlanet
Super Smash Bros. Brawl
Super Mario Galaxy.
OVERALL BEST SO FAR (in my opinion):
1) MGS4
2) BioShock
3) Gears of War