Ok, I totally know I am late on this one, but I actually had to really put some thought into what my game of the year for 2009 was. To be totally honest I did not play all of the releases from last year so Arkum Asylum and Assassin's Creed didn't get some play.  After getting over the initial hump of Modern Warfare  2's hype machine, the post holiday retrospective I have begun to realize that I don't enjoy MW2 all that much. Sure it is polished and well done, but I just don't find myself having fun. Mainly because of the frantic nature of the games.  
 
Battlefield 1943 comes out on top in my book for a couple of reasons. Firstly, it was my first experience in the BF series and it totally captured me in size of the maps. It is the size of these maps that really make for such an interesting new game dynamic. When the maps are as large as they are in that game the pacing of the entire game slows down a lot.  People aren't grenade and rocket spamming nearly as much as in other FPS's I have played this year and the maps themselves have almost no choke points on them that snipers can pin down.  
 
It is perhaps the one FPS game that I have played where I really don't get frustrated during the game. If there ever was a casual FPS BF1943 maybe it since all levels of players can easily get into it, have a good time and enjoy themselves.