It's a good start.
Well, I like the idea. It's a positive element that you can upgrade your car, get better guns, etc., but here's a list of things to fix:
-Make the dialogue at the beginning of each level a bit more natural. A super-tough gang guy isn't going to have the vocabulary of a professor.
-If you're on the left side of the road, make it impossible to shoot stuff on the right side of the road.
-Get rid of the Bazooka, and weaken the Vulcan Cannon. The Bazooka is useless when the Rocket Launcher is available, and the Vulcan Cannon is way too powerful.
-If you shoot something and it explodes, have some rubble remaining.
Good luck improving it, and as my summary of the game says, it's a good start.