Good graphics
Great graphics, maybe you could add some "moving" details to the backgrounds instead of just a picture, like, if the terrain at your distance is moving on x speed, the background should be moving on (x - 10) speed for example, its a nice effect and very simple to make
However, the "playability" is not alll that great. There are other games out there exacly the same as yours, with worst graphics and better gameplay, and pretty famous games actually, so what i mean by this is, focus on the gameplay... graphics help to get attention, but if playability do not match graphics, people wont play it more then once.
Anyway, i think you are in the right direction