I think a part of what makes the guitar games so successful on the Wii is that they come with their own controllers.
I know Wii-only guys don't like to hear it, but I think most who'd be interested in Wii core games have come to avoid them because of well-established control problems. I.e. you tell me that I have to shake my controller to attack, done, all excitement destroyed; it doesn't even matter anymore how awesome your game looks.
This is one of the reasons why I expect The Conduit to pull much bigger numbers than Madworld (3x first month was my prediction). It's in a genre that works great on the Wii and actually benefits from the controller.
I also expect Oboromuramasa to turn out more successful than Madworld, if we ever get sales numbers for either. Classic controller support ftw.