Tricky... but I'd have to say it's a three-way tie between Gears of War, Rainbow Six Vegas and Battlefield 2: Modern Combat. Gears has a great storyline and the game itself is so addictive, I've finished it 4 times already and now going for it on Insane, hard but I still love it. Rainbow Six Vegas is a great shooter, tactical too and it's great to play with my friends from work on Xbox Live. Bf2, well that's just amazing when you take it online, true carnage with 23 other people in the map. I love it.