Excellent!
Just beat the Nightmare level, oh my god so much passion! :P
6 Levels, not too easy, not too difficult, you managed to seize the perfect difficulty level. I don't want to talk for the entiere world out there, but that's what I strongly think.
Maybe you could add an easter egg when you finish the game at 100%. Even a crappy animation satisfy almost everybody usually, it's just always funnier and more exciting to play and beat a game when you know there's something special at the end. =)
Also, I find it great to control a wheel, not a biker or anything else that is frequently used, that was pretty original.
On overall, that's something great to play, original, and with a good difficulty. I'm waiting for the nest one!