I'm voting for Super Mario Galaxy 2, but I have to acknowledge how big Doom is. Alot of people credit Goldeneye as the mother of all first person-shooters, but Doom did it all before Goldeneye did and really introuduced alot of the things that Goldeneye became famous for perfecting.
Despite that, I can't in good conscious vote against Super Mario Galaxy 2. I think alot of people over-look SMG2 because it was a sequel and was released in a relatively short amount of time after the first (well, short in regards to Mario games). If it had been the first in the pairing it would have been seen as one of the greatest games of all time, but I think it seems to lose points for people because it was the "second go" so to speak.
Despite that, this is way too great a game to over-look and deserves recognition for how amazing an experience it is. It would be a shame to see it go this early in the tournament.