While the shape of them all are okay, I think some white highlights and darker shades would do wonders for you; at the moment they all seem very flat and dull, and as Fool showed with his edit, you can make these dramatically better by just raising the contrast a bit.
I'm unsure on anatomy, but I would say that it's off here and there an each piece.
A great start though--with enough refining, these will be suave. Keep pixelling!