I personally feel as though this game is underrated. The setlist has a lot of really cool songs (such as The Final Countdown, Fire, Grace and Breakout to a name a few), the visuals are cute and charming, and it plays just like Rock Band. I loved how they even managed to make the menus look both like Rock Band and like Lego (the tiger on the main menu is what instantly springs to mind).
Like others have said, it's all about the songs. If there are at least 10 songs on there you want, pick it up without hesitation. You can always trade it in after you're done with it (just make sure you export).
My only complaint about the game is that it loads a lot. Long loads too.