Obviously , none of these games are without flaw. I went with Call of Duty 4 because of the great SP story coupled with the fun MP. Infinity Ward effectively took away MP Spawn Camping by just bringing the meat right too the Spawn Campers themselves with some of the worst MP spawning I've ever seen in a game. Don't feel like running around and looking for a grenade to place under your scrotum ? Have No Fear, COD4 MP will place one there for you right when you Spawn at no charge. Brilliant
Honrable Mentions...
Mass Effect - Like playing an excellent Sci-FI movie - graphics, weapons, music, and galaxy exploration was killer, extreme moments of slowdown not so much. I won't feel like taking an elevator anytime soon. Sex scene with Alien made me feel all dirty.
BioShock - Great Artwork and Gameplay ( The Circa 1950's era touch was awesome ) . Once it was over I wanted to play more, but didn't.
Orange Box - Best Bang for the Buck, it's been neglected because I've played through the story before on the OG XBoX, Need to go back and play through the whole game.
Worst - Halo 3
Assassin's Creed
All in all one of the best years in video gaming I've ever witnessed.