Here we go, a good reason to own the Wii. This game was one of the best 3D Mario experiences I've ever had. It was a solid title to this great series and definitely warrants a play. Why? Because this game has what many Mario games needed. Challenge.
Getting through the main story of this game is not the difficult part. No, beating the big baddy (you can guess the last boss) is just the beginning of the fun. Collecting all the stars is the hard part. Where in typical Mario games, you just have to look high and low for them. In this, you have to look everywhere, literally. With many of the galaxies being fairly large, these can be anywhere.
Sure the levels may not be hard, where is the difficulty? Comets. With the comet system, the levels get harder or different based off which comet is there. Sometimes they are nice relaxing "find all the purple coins" kind of challenges. Other times it "time limit, go" kind of challenges. You always know what you need to do but it does add to the fun.
I would say that this is a must own for the Wii but most people that own a Wii have this already. Sure the camera can get goofy at times. You can't blame it when it suddenly is not on the same plane as Mario. Still, this is a solid title...only trumped by the sequel.