Thiese are some damn sweet sprites. I love the sprites, the style is so cool and cute! I like how it's simple, yet detailed. Nice work.
I can see what you mean about the walking animation. I think the problem might be that he is bending his knees too much. Looks like he's walking with his knees up to the waist. When walking relaxed the legs are a bit more outstrectched. Changing this would make the sprite slightly taller than the jabbing (except the upwards jab, then) and idle ones I think. The movement of the arms in the walking animation is really sweet though.