Madden 2005 - A revolutionary NFL game. Introduced the hit stick, and is still the only NFL game I play, despite having '09 and '07 as well.
NBA 2k11 - I haven't played 2k12, but this was a really good game, especially compared to 2k10 and NBA live 10. It really is a great game.
Angry Birds - This basically introduced the idea of a simple game being addictive on a modern mobile device. How many iphone/ipad/android apps are up to this quality. Its like a modern day tetris or pac man, since its had that effect on gaming.
Infinity blade: The best game on the iPod, in terms of graphics and gameplay. The storyline was pretty damn good too. The only reason it isn't the most bought iPhone game ever is because it costs $6. Its inspired a second game, infinity blade 2, as well as the wildly popular free game Blood and Glory, which has no storyline, and just the game play and graphics, and peaked at #1 on the app store and stayed there for quite a while.
999: 9 persons 9 hours 9 doors: I think this is the best novel game I've played. Its better than ace attorney, because despite the fact that you don't get to yell out OBJECTION, you have different story lines, and different variations based on them.