From videos, it seems like the levels are somewhat sparse, and that the game is really means as a multiplayer "party" experience ... much like Four Swords Adventures or Mario Party. You can play those games solo, but what's the point?
What I really want is a true single-player console platformer, like Yoshi's Island or Super Mario World. I didn't really care for New Super Mario Bros. on the DS ... the level design was not exactly memorable, and the save system was unnecessarily complicated.