The sprite is quite nice, but lacks volume. You might want to add a darker shade for each colour, so you can open the door to sub pixel animation, which means animating the frontier between the shades inside the shape of the sprite, without having to move the outline. It allows a lot of subtlety.
As far as the running goes, running will throw your chest from left to right, so having a fixed chest while running is really unsettling. The shoulder should translate the rotation of the chest. I'll ad that the hand holding the sword being totally still make thing really hard to believe, specially when the sword does move. The legs aren't bad, but the motion lacks acceleration and deceleration, it's too linear. Ease the motion when the leg get to the full front and back position, to sell the weight and inertia.
Hope it helps!
Keep up!
- Skaz