It's just fun
It's probably the funnest game I've played. There's a bunch of cars you can choose from. It gets really fast at times depending on the song that you chose, any song can be imported and the game engine creates a track for it, that's why it's so fun, you can choose a new song or keep trying to get a high score on the same one.
The online High score board makes it even better, trying to outdo everyone on your favorite song is very entertaining. I've bought many of those 5 or 10 dollar games off Steam, but this one is probably the best I've bought.
The fact that the song you choose gets turned into a racing track style thing is what makes it the best, it's not like one of those games with pre-made tracks. The best I can describe it from games I've played is Guitar Hero meets Bust-A-Move meets F-Zero, or if you're using one of the mono cars it's guitar hero meets f-zero meets tetris where the gray squares are the holes.