It's good to see you animating. I recently made something like this, but at a different camera angle. I think for a more powerful hit, you should add less frames to the punch itself and more frames to it's starting and terminating positions. Right now it doesn't look so powerful when the hit is being displayed over the course of like 4-5 frames. Everything else looked pretty good, the back has a nice little snap to it, but his legs are a little shaky. Especially his back leg towards the end (probably because he moves too far forward for his foot to stay in the same spot)
Either way I loved your BBODD entry and it's cool to see you animating something.