Can be improved.
I know 3D games are tough to make, and kudos to you on making a pretty good one.
Now that you're familiar with 3D modeling (hopefully), you can probably make the sequel have cars and tracks with more polygons. Make the turns smoother, etc.
The handling on the last car is perfect. Too good. The last car should be more like a jet, than an F1 car. (Last car has too much handling, make it a lot more stiff). The red car should have handling like the green. The yellow car shouldn't be able to turn more than 15° at higher speeds, encouraging people to actually use the brakes.
Which takes me to my next point. Firstly, the turns are mostly impossible to get at full speeds, which is not a bad thing, but when combined with the overly sensitive handling on some of the cars, if you slow down a little you basically slam into the wall you are turning to. The walls need to slow you down a lot more as well. To a near complete stop. In this game, you can hit the walls and still maintain nearly full speed making the unmentioned brake button useless. So, make the turns a little wider and smoother, and make some of them force you to brake.
The cars all go at nearly the same speed. I saw no major straightaway differences in speed, the only thing I saw different was that the yellow car accelerated a lot quicker. So your "speed" is more like acceleration, not speed.
The AI is also badly programmed. They turn right and hit the walls before the turn, and if you slow down for a split second, they fly right by you. So, the same rules that apply to your car should apply to the opponents, no?
Enough about the flaws, how about some things you should add? :)
I think an upgrade system would be nice, like in Fatal Inertia, there are 4 types of main ships (neutral, a high speed low acceleration low handling tank, a high speed high acceleration low handling frail ship, and a lower speed high acceleration high handling car) look at some videos to see what I mean, and you can upgrade those ships parts. So what I'm saying is have distinct ships that you can upgrade.
More courses would be nice, as well as a campaign and time trial mode.
But anyways, although this game has it's flaws, it's still a great game. 4/5