Looks great! Nice and cartoony movement.
One stylistic approach would be to enlarge the size of the fist on the action frames. Alex Kidd and Kangaroo sort of did this, and loads of old cartoons like Popeye and Tom and Jerry. Think it works great for sprites especially though, shows more change, and gives a bit of an idea of hit-area. Usually swords have some huge smear that works like this, the little fist seems a bit fiddly in comparison.
Obviously it might not match up with the style you're aiming for, but you might be surprised if you try it out, and you can adjust the exaggeration to whatever suits.

Not sure if this technique has a name, but I'm sure PixelPiledriver re will know if he's reading!