the player hitbox (or maybe the rocks) don't seem to be fair (the hitbox seems larger than it should), a crashing animation could be a nice addition, and most of the game of this type generally includes more controls than left or right (accelerate, slow down, etc..) and have a time score rather than a "number of things passed" score.
graphic wise, it is as you described, needs more work.
I suggest you see exemples like rad racer or hang on to inspire from them.
nothing else to add, hiscore 32
Run fine on my phone too, and would be nice if the blocks wouldn't move until the GO