It's a great game. I like what you've done with then graphics, having all the tracks exist as minis in large-scale environments. The old-school style doesn't ruin this at all. In fact, it helps it.
The game controls well, which is important in any game that depends on speed. It's fun to play. The upgrades start cheap, but even when they get expensive, you're making enough money on the tracks to afford them. The cars are affordable with just a few replays. There's a constant sense of advancement, and the upgrades give noticeable payoffs.
I do have two problems: first, it seems as though the laws of physics affect the player, but not the other cars. I could be wrong about this, but the other guys don't seem to respond at all to contact. They don't crash, they don't slow down on curves, and they don't lose speed when they make contact with another vehicle. This is a problem when a rival decides to side-swipe you or push you aside, and you lose speed but they don't. Worse, you can't do the same thing to them. If you try to push them aside, you lose speed, but they don't. In addition, this makes it possible to ride the bumper of another car while everyone shoots past you, and continue doing this for the entire race, because the dude you're riding never gets pushed aside. In all, it amount to a horrible imbalance in the competition. The other cars drive with robotic precision, and they aren't affected by poor conditions. But you are. You can only beat them through sheer speed.
Second: track 7 is absolutely brutal. Track 8 is fine. I came in 1st on track 8 the first time I tried it; track 7, I'm lucky if I can finish in 3rd. In fact, 7 might be one of the most difficult tracks I've ever seen in a game like this. The curves are so violent and sudden that you can't help but be thrown left and right into the obstacles no matter how careful you are. Worse, the obstacles are much bigger than they are on the other tracks, making it impossible to avoid them even if you're at the edge of the road, not off it. The only way to get through it safely is to use a slower car and drive at low speeds, which ensures that you can't take 1st place. I have a fully upgraded purple 160 with 1st place on every track, except 7. Maybe I'll keep trying.
Ultimately, this isn't anything new, but it's a strong racing game with solid mechanics and good controls. Very enjoyable, but you should think about a few balance issues to the gameplay.