This is a tough one. Lots of good games this year.
Ninja Gaiden is definitely in the running. For me, there's no better action game ever made. Its beautiful. Its old school with new technology. Just a great game.
Fight Night is a game that could have been in the running, if it had a few more tweaks. The parrying has to go, as well as the button control. Put a better creation mode, and the ability to edit boxers stats as well. That being said, its the best boxing game I ever played...and my online matches with everyone here was some of the best online gaming I've played.
RSC2 is the finest racer I've played. It also feels like the most together title on consolers this year. Its hard to explain, but everything about it works. It feels so damn solid.
In the end though, I give GOTY to UT2004 . Amazing agme that I would still be playing if I was sickened at my poor performance on onslaught maps. When I get a better pc, I'll be reinstalling this son of a bitch. One of the best FPS out there with a huge amount of mods. So much fun when your in a game with people you know.