I have two issues with this otherwise fantastic game.
Level design is better than its ever been with clean and crisp graphics that you can't fault one bit. No clipping. No Weird blocky shapes. Nothing that could possibly ruin the experience at all in anyway. Although there are times that I wish the Wii was slightly more powerful... The platforming is what you'd expect of a Mario game and the difficulty while harder than Galaxy is, in my opinion just right.
The music is a full orchestral score and compliments the game perfectly. Although when you start whistling the score at work, which you will, it can become embarrassing...
The controls, however is where I take my first issue. The set up is the same as Galaxy which is fine however it is not as responsive as I would hope and this can cause problems. When I press A to jump I expect it to do just that not think about it and then do it or wait untill its too late and I've slid of the end of the map.
Finally the story. This is the biggest problem with the game for me. There have been two kinds of Mario game since 1998 when Super Mario really defined itself. The Super Mario series which is has a refined story line and a hub and spoke system and the Super Mario Bros. Series which it the side scrolling with few if any story elements and a Map based system. Galaxy 2 seems to be an attempt to merge the two. With the spokes disappearing, the levels becoming shorter, a Map being introduced and the story becoming an afterthought. And I'm not sure that's the way to go. Further the story is a parallel of the one told in Galaxy its not a true sequel and that just seems rushed to me.
That said...
Gameplay 10
Design 9.5
Story 8.5
Get this game 9.0/10