Sculpt the jawlines of your characters better, they look too rounded. Observe the proportions exhibited IRL and give your characters more life-like properties. Some quick proportion tips, the arms should be about 1/5 the width of the torso, head 1/7 of the size of the torso, armspan is the same as height, hands should reach below the waist, almost to knees, and the legs should always be longer than the arms.