I really only played games for XBOX and DS, so I will only label these two systems.
Best XBOX 360 - Mass Effect 2
This was the game I was most excited for for 2010. I absolutely loved the first game, and this one does not disappoint. Sure mining planets for minerals became annoying after a while, and the powers/abilities were immensely scaled down, but these didn't hold it back to being an amazing game. The downloadable content keeps you coming back and really expands the story farther.
Honorable Mentions - Red Dead Redemption, Halo Reach, Call of Duty Black Ops
Best Nintendo DS - Golden Sun Dark Dawn
I have been waiting for this game for several years now, and I was overjoyed when I found out it was becoming a reality. After the long wait, I'm pleased to say that this game delivers in every aspect. It does not disappoint one bit from it's amazing two predecessors, and I will be playing this for a long time for sure.