The perfect game for die hard Nintendo/Mario fans everywhere.
The animation and controls are super smooth. The motion sensitive controls are very responsive and quick, some 3rd party Wii games have some sluggish response times but Nintendo knows what they're doing (eg: Metroid 3, Twilight Princess).
The game itself is great, the level set up is somewhat like Mario 64, where you begin each session at a certain area, where it used to be the Castle, now it's a space station-thing inhabited by floating/talking stars called Lumas. Rather than jumping into magical paintings, you enter observatories and travel to new galaxies. Each level is spherical rather than the traditional orientation. This might need some getting used to but it really adds to the gameplay. The boss battles are classic Mario and the semi-Multiplayer capabilities are as well.
Every system has one game that makes buying the console worth it, for PS2 it might be FFX, for Xbox it was Halo, and for the Wii it is Super Mario Galaxy.