Last level...
...was fun and challenging. A turbo button would be a nice addition! You know, like have parts where you have to turbo to make it over a pit or something. The whole changing the colors thing... hmmm kinda slows things down in a way, but makes it more interactive... like that level where you could pick the path.
Also, a vertical boost button would be cool too... like an anti grav or reverse grav thing... where you could go on the ceilings. Keep at it!
Oh and a very big crit: not enough sound effects!!! I'd like to be able to hear the bike rev up and the sound of the tires hitting the ground when it lands from a big jump... or crowds cheering everytime you do a successful back-flip.... then I'd have given a 10 for sure, although it was short (I don't mind that so much cuz it has replay value with the times).