Keep making more
The physics feels just right. I'm betting that you guys built a very detailed engine to emulate the movements. Most of the points goes to that. Oh yeah, one question, does the camera movement actually indicate altitude change? Kudos on the cam directing, if it can be called that.
But as the users before me has said, you should have more options or more variety of cars. Making different performing cars is possible as you did make two different cars that performed differently. So you could make more cars in a second installment.
If possible I would like to see a tunable setup; users could tweak the performance. Also, a minimap would be helpful. The turn indicators are good, but a minimap coupled with it is even more helpful, I could be more aware of what corners and obstacles I would be facing and in what angle. A wrong way indicator would be nice too, since there were moments where the car was reset, at a position where I'm unsure where the correct way is.
There is a bug I noticed in the game the game where the could actually cut through the track at places where there is an obstacle or just cut through another part of the track.
I didn't really mind the absence of any background music, I just played my own. Actually, it's really better to keep it simple. Less files, less loading time and sound files are huge.
All in all, I think it was an excellent game, it gave me a great experience and it showed that there is a big potential to make this game even better.