One of the best platformers of this generation so far, and definately the best on the Wii.
What sets this game apart from all the other platforming-focused games is shape of the words; instead of having flat or hilly horizontal worlds to explore, Nintendo opted to go for a bunch of worlds that have no boundary, but nor are they infinite in size. I would call them spheres, but they are rarely spherical. For example, the first galaxy you come to, the Good Egg Galaxy, starts off with a planetoid with a tower that you can run up. It's a weird feeling when you see Mario running up a vertical wall as easily as if it were horizontal. Weird, but fun.
This often makes for some tricky platforming. The camera does not stay looking over Mario's shoulder, but nor does the D stick change to accommodate the new position Mario is in; YOU have to accommodate for it. This is funner than it sounds. You find yourself smiling the whole time.
The presentation is equally as impressive. Controls are nice and tight, even those requiring the Wii Remote pointer, and the graphics are better than Super Mario Sunshine (though you'd literally have to juxtapose the two to tell the difference; look it up if you don't know what that word means).
Now, you may ask "if the game is so good, why give it a 9.5 and not a 10!" Well, the game isn't perfect. The one place where the game falls flat is the lives system. Really, I don't see what the point is. When you run out of lives, you just get sent back the the main area, plus you loose all but three of your lives whenever you go to eat dinner. It's annoying and pointless. I understand that this is a minor flaw that doesn't subtract from the overall quality of the gameplay, but tens are only supposed to be given to games that are absolutely perfect.
Still though, this is a phenominal game that you will really want to run out and pick up. Combined with Zelda: Twilight Princess, Metroid Prime Corruption, and Zach & Wiki: Quest for Barbaros' Treasure, the Wii definately has a good library to justify its meager $250 price tag.