5) Jak 3: I loved the free roaming of the game, and the mechanics/combat was so fun
4) Dark Souls: Some of the best multiplayer I've ever experienced.
3) Kingdom Hearts 2: This game is the result of my mom driving me to EB. The story had me going lolwut at first, but once I got into the game it was incredible. Going into different forms was awesome, and the only downside to this game is that Little Mermaid level.
2) Fallout 3: This game was truly perfect for me. The setting of the game, a grim radioactive wasteland, was so incredible. The world was huge and completely free to explore. The radio music was fantastic, and pairing it with a futuristic 60s lifestyle was interesting. I loved simply exploring the wastes with no objective in mind.
1) Halo 3: This game was the reason I got an Xbox 360. I think I had at least around 1600 custom game sessions. Playing crazy game types with friends on Friday nights, those were the days.