the way you have the motion blur slowly fade out is wierd, and makes it seem like you dont understand what it represents.
heres a really bad 3 frame example

the blur in frame 2 is supposed to show that within the time of that single frame, the line is swinging through all that space, its so fast that we are sort of seeing it in all those positions at once, rather than changing the timing of the animation so that we fit multiple frames in the time of that single frame. But once the line reaches the end, we dont need to show that blur anymore, because in the next frame we arent trying to show that the line is occupying all that space still. It already moved through that space. By getting get of the blur it appears faster.
also, if this is for a game, I think you need to consider a different type of swing. Your attack only extends like 8 pixels in front of the characters body. Youre going to have to stand so close to the enemies to hit them its going to be very frustrating for the player.
the start of the animation is a little wierd too. how he starts the swing by moving the sword a small distance very slowly, and then suddenly very fast. I know in an earlier thread pixelpiledriver (I think) talked about slow in and slow out for animations but I think youre implementing it wrong.
Take the sprite at the top of your last post for example. The motion starts out slower because he begins by lifting the sword. The swing itself though is fast and fluid, a single motion. The blur only lasts 1 frame so it seems fast. Then he holds the sword at the end position an extra frame to slow out of the animation.
Im not an animation expert so maybe I explained some things badly or wrong, but hopefuly this helps.