Ok.
1st. It looks like the whole upper body is just swiveling. Ok? Here's how we fix it. Instead of just moving the arms forward leave the shoulder as is, and bring the forearm along with the fist up and use darker shadows the more the arm bends in the elbow area. Mmk? :]
2nd. The legs look like they are sliding forward. Add an extra frame or so of them lifting up. Then going forward. Mmk?
Other then that I pretty much like it.