Despite the fact that the game doesn't appeal to me, as a gamer I think this is a game the Wii needs to extend beyond its current niche appeal. It may be a large niche, but its a niche nonetheless.
What I feel about the Wii is that Nintendo had adopted a motto something along the lines of "appeal to everyone." However, in that fervor, they ended up not trying to "appeal to everyone" but "appeal to everyone we haven't appealed to before" (i.e. the casual crowd). The Wii, while an amusing system with some decent games, has been running strong on a casual crowd, but has left the "hardcore" audience out in the rain. Now are "violence" and "hardcore gamer" equivalent? Well, some people seem to think so. But regardless, I think MadWorld will open up that "appeal to everyone" mantra a little more and make the Wii have TRULY universal appeal.