So it's a racing game without steering, and without actually racing? Since there is absolutely no pressure to actually get through it fast (aside from the constant speed of the car). It also doesn't really feel like the car is going fast. Additionally, although said in other comments:
Hitboxes are brutal when steering, since you can hit your back against a wall when you turn, and then crash. Also, that the camera auto-scrolls with the car, but the gun doesn't, makes it hard to line up shots. So I'd either make the camera scroll with the gun, or make the gun also move when the camera moves (so it'll stay at the same position on the screen if you don't press anything).