MadWorld actually did pretty good the first week of sales; SEGA's VP of marketing has already spoken to that. I think the true test will be seeing whether or not the game has long legs as time goes on.
It's also an M title, which does limit numbers a bit, but I think the crazy violence is the much needed barrier that sets it apart from the shovelware "let's bake a cake!" games that are becoming all too prevalent on the console.