It's the best platforming of any 3D Mario and it's highs are the highest in the entire series, but in the interest of making some counter points, I also think the game has the weakest endgame, and that the comet stars which make up almost half the content are honestly, for the most part, shit.
It's basically 60% one of the most perfect games ever made, 40% shit filler. Obviously you don't have to do all the comet stars to complete the main story, but I don't much like having to avoid main content just to enjoy a game. A great game, though, obviously.