Graphic is coherent, its good. But I think game is too frugal. Maybe you can add some object and when you his it arrow bounce, or gain additional projectile speed or slow down, or gain additional point.
The ui of the game is horrible you shoud try to mimic somo ux and ui from other top games. The difficulty curve is too pronounced, the first dragons should be easier. The launch physics are fine, but you should give more feedback on the throwing power.