It won't sell better than MP3, and sure as well won't be rated higher.
You can draw your own conclusions as to both, based upon a fair comparison between the two games, despite the differences in development times.
Frankly, I don't see what is so special about the game that it would make it worth my time over all the other FPS/shooters I've bought or will be buying in the back half of 2008 (Gears 2, Resistance 2, L4D, Crysis Warhead, CoD5).
So it's being hyped by its developers as having the most sophisticated effects yet seen on the Wii. That really means next to nothing to anyone playing on any other platform. So unless there is something else going on in terms of game play to make it stand out, it's not worth my time to play, much less my $50.
It pretty much remains the great white hope for the Nintendo hardcore faithful. But as it's already been made quite clear what sells best on the Wii, the multi-million best seller predictions are most likely sadly misplaced.