The idea of the attack was that the final punch was supposed to be super heavy, and I based it a bit on one of Alex's attacks from Third Strike.  

That definitely looks a lot better, though.

finlal is right, the hit should be way faster,
nice animation besides that :)

Good animation. Very smooth and clear.
But there's one big problem. It's too slow during the hit. I'd suggest deleting 3 frames - 33,34 and 35, for the sharpness.
That way hit feels much harder, I think. Also added one frame for backing up to compensate for deleted frames a little.

Those are minor nitpicks, but they can make your great animation even better, imo.