I don't understand what happens with his legs in the slash.. Is he facing his butt to us in the first and the last frame of the slash? Then how does he make the steps in between?
Also, he might lean over more to the camera mid slash, move the whole thing down a pixel or two midway
The motion blur is a bit strange in some places. In the first frame it seems to be pushing from the sword, instead of pulling. Then at the mid part it is very far away from the character, as if his sword got muuuch longer, and then in the end it disconnects from the sword...
I tried to quickly fix the things I mentioned above, except for the legs.
Good luck