In space... no one can hear you HAVE FUN
It gives you plenty of hours of play time, as there are WELL OVER 120 stars to collect (if you plan to squeeze every ounce of gameplay out of it).
Co-op mode is an interesting addition, as it is welcoming, but doesn't hinder the gameplay, and can potentially make you do better if you and your partner are strategic.
All-in-all, this game is a wonderful experience and I urge all Wii owners to buy it.