Well, a pretty nice game you've made. The graphic just looks fine, no need to add more (would just lead to lags on older PCs). But the steering ... much room for improvements. The chosen controls are a good way to control something from a FPV. but used in a top-down view it just leads to frustration. I would recommend using a classical coordinate system control instead of trust+direction.
that, and a mini map, and you have a really cool game.