QFT
Having said that, my vote is Halo3.
I think wth Halo2 being as popular as it was/is and this mostly based on the online portion (as most considered the single player to be a huge let down), I think Halo3 will continue this tradtion and the online portion of Halo3 will be gold. The single player MAY not match the quality of the original and I would be dissapointed if that were the case along with many other Halo fans, but I don't think it would be enough to cause negative sales for the title.
Now If they screw up the online portion, all bets are off.
Side note - I agree with Joshua on the sports league football 2k entry. I think it has the
potential to be the biggest game for me this year but I could also see things not going as well as hoped or small things ruining the experience (unlicensed, poor production value, etc) If they do it up right though this could at least push EA to try in this genre. The NFL license will probably bug me but if the action is anywhere near as nice as I hope, I'll be quite happy with this game (along with many others this year).
I am anticipating that game along with every other on the poll and a few others not listed. It's a good thing I have unlimited rentals! I would go broke this year alone on games!