I really think NSMB U (and 2) suffer from the same problem as the Wii version of Animal Crossing. No, Nintendo, making your new games look very similar to old ones in order to be innofensive to consumers isn't a good formula to get consumers to jump at new games, espeically if they're supposed to move consoles. NSMB DS was the return of 2d Mario after years without anything similar. NSMB Wii was the return of 2d Mario to consoles and the first one with 4p co-op.
NSMB2 and NSMBU, IMO, completely misread what made those games such break out hits when they decided to make them look and feel similar to the previous games in the NSMB series. They needed to stand out, not look just like the games that people already had.