pretty solid animation, I'd say. There's just something a bit awkward with the shadows on his back ... something "jumpy" that I can't pinpoint precisely.
You may also want to add some pendulum to his left fist (the background one) to avoid that "punch-at-every-step" effect you have right now.
... wait ... legs, and the other arm ... everything looks "jumpy" on that frame that moves the fore arm backwards. Is the animation complete ?
Oh, and maybe his ear should follow the overall head twist movement