I'm shocked at how good Halo 4 has turned out to be so far, so probably that. If it weren't for the whole end scene fiasco, Mass Effect 3 would have been my GOTY easily. My most anticipated for this year was ACIII, but the Desmond storyline was really underwhelming.
ME3 is mine so far. I've played just before the end and have stopped in order to play the upcoming Omega DLC that comes out 11/28. Runner up would be Xenoblade, the game is jam packed and incredible. Too bad it isn't available with the original high-res graphics.
I will someday get AC3 (still need to beat Brotherhood, playthrough Revelations) but I'm still completely uninterested in the setting.