And aside from the mixed resolutions, the big thing here is your animation is happening at one speed, each new position of the legs/arm/sword covers the same distance as the last. For a more natural motion, remember that the sword swing is actually the shortest part of the motion, it goes by in a blur, so you want more frames before and after the swing. The easiest way to learn this "easing" motion is to study other animations frame-by-frame. You'll start to see what I mean!