Hold The Presses! Super Mario Galaxy 2 Scores a Perfect 10 from Gamespot.com
First Mario game to do it, as said by user Justplainlucas.
Ign scores it a Ten as well.
The two closest wii games in scores is the original Galaxy at 9.5, Brawl at 9.5, Smooth moves at 9.1 and Resident Evil 4 Wii at 9.1