I got the game for Christmas and played through it with two of my brothers. Somehow we managed to skip World 7 (and half of World
while still beating the game. Afterwards, I went back and collected all the star coins (mostly by myself) and replayed the levels I missed (mostly with a partner). Somehow, I've already done everything there is to do in the game (the game itself said so!). All in all, the game was very, very good. I've heard the DS game isn't up to the series' par (though I never played it), that is hardly the case for this game. The levels are consistently creative and challenging, the multiplayer is a blast, and the bosses are actually pretty good.
The only real complaint I have is that the controls for picking stuff up are a bit too finicky. Sometimes when you want to spin you pick something you don't want up (eg other players), and sometimes when you want to pick something up you end up spinning. Also, you can't pick up stuff while underwater, despite being able to carry items while underwater.
