My first impression was that it needed less foreground and more of the legs and shoes at the top (I kept trying to scroll up to see more). I think that would make the play between the shadow and shoes even more noticeable. Great idea. Very fun and happy feeling.
I'm not sure I'd get the same sense of movement without the motion blur. The fact that the shadow is seemingly still is the perfect resting place for the eyes before getting swept away by the movement again.