This is, along with Super Mario Galaxy, arguably the greatest game on the Wii right now. It's simply up to your preferences on the number of dimensions you like your platformers to have. If you have ever liked a Mario game, get this. If you like gaming cooperatively with family and friends, get this. The only reason why you shouldn't get this is if you simply hate Mario or platform games.
Even then, there's just something about the impeccable level design that could make you reconsider. It's the perfect combo of old and new. Simply put, New Super Mario Bros. Wii is Nintendo's newest masterpiece.