Very good
It was an interesting twist to put to one of these gravity controlled driving games. It was fun, but could use some improvements. First off, it was a bit too easy. There should have been some more complex levels that really require a lot of thought to pass.
Secondly, having only one song got old really fast, especially since you made it restart after each stage, most of which are finished in seconds, so you only hear the same part of the song over and over again.
Thirdly, while I had fun playing this game, it was kind of stale. Some power-ups and or enimeis would have been cool. Also, an option to customize the bike with different parts would have been really cool.
Overall, it was very well done.