The game is created by Sega with the support of Myamoto.
It's not because you have low expectation for this game that's the same for everyone. It's sure it won't have the hype of Halo, but don't forget that Mario and Sonic are two strong names and matching them in a single game for the first time can easly appeal to the gamers who saw these two character fighting each other in the 90, that's what we call nostalgia. And if they create this game like Mario Strikers, Mario Tennis or Mario Golf, he can have a greater appeal to the casual crowd than Halo.
There is other factor to, there are many great games comming this holiday on each platforms. In 2004, the Xbox had Halo 2, PS2 had GTA, the GC had Metroid Prime 2 and the PC had Half-Life 2.
For 2007 :
360 - Halo 3, Bioshock, Assassin's Creed, Quake Wars, Mass Effect, Too Human, GTA, Madden, COD 4 and others...
PS3 - GTA, COD 4, Assassin's Creed, Madden, Heavenly Sword, Lair, Uncharted and others...
Wii - Mario Galaxy, Smash Bros, No More Heroes, Resident Evil : UC, Metroid Prime 3, Mario and Sonic, Madden and others...
It's not the same scenario than 3 years ago. So anything can happen.