Well, he still needs some motion to make it less robotic.
As I understand its one two punch which is seems to be a copy of Firen punch, by copy I don't mean a bad thing.
While this animation have many frames, it lacks fluent movement. I suggest making him move more than it is already, would be great and add more new parts instead of copy paste.
Here is a quick template for what I see could look better.
Mostly this is based on Firen's punch frames but again, why not to reuse and get a better result than try on your own and make it less appealing?
One suggestion. Before making a sprites, for animation and simple one sprite, use base. This will help you to fix the flaws.
I gave some attetion to your sprites. Problems are that he looks like action figure toy. You can bend just some parts, not making it have natural body bending. Allow separate parts move even if those parts are not the main objects of the movements.
Example.
This gif. Made by me. Sure, last kick looks buggy but lets focus on the 1st and 2nd punch.
©
//DO not copy my gif animation or style and design.
Some tips on punch sprites what I found out while spriting.
Punch frames if its three frame punch.
1st frame legs makes a movement to concentrate energy into them. Makes a little crouch
2nd frame moves forward while punching which is actualy same in real life except for certain style of fighting. Moves Aleg to the front while Bleg stands in the same position.
3rd frame Moves Bleg towards the Aleg while closing the move. When he finishes his punch, he again moves leg closer to another.
Example
http://sketchtoy.com/65163949
While making punch frames. When making all two or three punch frames, think not about the one frame, think about the all frames which are involved in punching animation sequence.
Another helpful tip to check if animation is good is to put frames in complete sequence like this one have
the one I showed earlier.