Very nice! I really enjoyed the Medabots series, so it's nice to see something inspired by them. I'd like to see some more work done on the shoulders though. I'd either try swapping out the gray ball-joint piece with the corresponding socket piece (
http://www.bricklink.com/catalogItem.asp?P=57910), or change the way the socket joint is attached to the arm. (I think swapping the part would be your best bet, since it would allow for more freedom when designing the upper arm/shoulder.)