Let's recap the last 2 years: Halo Wars - Crap. ODST - Short, had to get dlc if you wanted to play more than 2 hrs, so - Crap. Every Halo game has been pushed back in development, ever - Crap.
Although the games are good, I can't justify it being the best game of the year in any year. It would have to be 12 hrs long in play, contain 20 different styles of weapons, actually have a better plot device, move more fluently, have a wider array of aliens, actually use the engine on which it runs, and possibly offer a multiplayer that didn't suck dog bollax to make me cough up the $60.00 USD they want for a game which will obviously be short, have few weapons and levels that will require me to spend 90,000 microsoft points in dlc to actually enjoy the game.
All of this to say, there isn't a chance in hell it will be game of the year, even on the Xbox 360. Microsoft should start drug screening their marketing department so they don't go off and start ranting like a bunch of dumb bastards, saying things that they will undoubtedly have to live down.