The nose should be visible from the side.
The shading should be from the center of the top of his head, and not to any particular side.
The shading on the shoes shouldn't look the same from every angle. From behind, since there's the character's shadow, it should be darker.
The top of the eyes could be shorted off a pixel or two and made more round.
The hand that faces the screen in the back-diagonal frame should be more visible and bigger than the opposite one.
The tail in the back-diagonal frame should be at more of a downward angle.
The white fur on his stomach is smaller in the middle-front frame than it is in any other one.
Why is his head asymmetrical? It just looks odd.