In a word, delightful. Every stage has some kind of gimmick to it, and it doesn't quite so transparently feel like it follows the "introduce, iterate, test" structure that became so familiar in some of the NSMB games and Retro Studios DKC games (though it probably does follow that structure, it's just not so obvious about it). What maybe hasn't been said enough yet is that the online features let you cheese out difficult sections in stages like one might be able to if they were playing with local multiplayer, even if they're playing alone. That's kinda neat, though it does feel a bit cheap, at times, so it's a good thing it's opt-in.