
Played it for roughly two hours before I gave up for awhile. I've got 11 stars so far and I've thoroughly enjoyed every moment of it. It's a little annoying I pretty much ruined the first set of levels by watching all of the videos flying around. But nonetheless - this is already, without a doubt, the best Nintendo Wii game available. The graphics are incredible, may I add.
Feels like very authentic Mario and the gravity thing seems to work straight away. There's no confusing headaches while you adapt to a new slant on the existing system. The quality of the camera really helps matters too, I'm so relieved Nintendo pulled that off. Any niggles at all would probably ruin the entire experience.
My only disappointments? I've played for two hours, not really making a point of collecting too much. Yet I have 25 lives. Also - I'm already over 1/5 of the way through the game if I don't care about getting all 120 stars (I do, but still). I guess there's a limit as to how long the concept can stay completely satisfying, overall I'm glad they chose to cut it short instead of over running it.
And you can definitely see where their time went instead. The design is flawless. I was worried the game would feel very fragmented and that it might be reflected in how the game is set out. But everything is brilliant! 
The ray surfing was a laugh - but not as hard as people made out. I would have got it on my first try, I past the finished line and then suddenly veered of the track because I pointed my remote away from the screen. Took another try before I managed to finish it legitimately. 
The Sweet Sweet Universe thing - I did on my first try. Bit of a let down really, I was quite looking forward to one of those frustrating yet addictive challenges Sunshine is so famous for. Ah well, I'm sure there'll be more where that came from. 
10/10