Ok. Dude. Seriously.
I like your ideas. There were some obviously good ideas in there (a little inapproapriate, but good nonetheless) such as the flashbang: quite original, and pulled off quite well. The music: I love it. I'm gonna go download them after this review in fact. I feel it fits with the racing theme too, but that's personal opinion.
Now for what need improving. Firstly (sorry, another personal opinion), I think the green car should be the beginner's car, and the red the intermediate. The 'Expert' cars, however, are just impossible to play with. I mean it. You need to press and let go of the accelerater constantly if you're going to live. If that's what you intended to be 'Expert' then you did a great job.
An alternative to slowing down the expert cars would be wider roads.
Something awesome would be a little bit of drifting. That would suit the expert cars greatly. Maybe only the expert cars can drift (hmm... motivate everyone to try them).
Looking forward to your (possible) sequel. Keep working on it!