We've heard Sonic Mario fans grumbling about the taming of the characters' special powers (i.e. Sonic doesn't run ridiculously faster than Mario), but if you can get over your fanboyisms this looks like loads of fun.
People are also moaning that it's not crazy enough for a Mario and Sonic game - but notice the flames at the feet of Yoshi in one shot, and Mario in another as they race. You don't get flame-feet turbo boosts in real life, do you?
It looks a bit strange to see Dr. Robotnik (or Eggman, as Sega likes to call him nowadays) lining up for a civilised race against Sonic, but the range of events and Wii Remote controls will make this a great multiplayer party game. Better than Wii Sports? We hope so...