It is a fun game, the setting is lovely, stellar music, interesting mechanics that have been upgraded from Super Mario 64, but...
One big point against it is the INSANE difficulty in some of its levels, most notably the "secret" levels. Besides the original Super Mario Bros. 2 (aka, the "Lost Levels"), this is pretty much an officially made Kaizo Mario game. That for the most part, is why I don't give this game 5 stars.