His right arm looks a little bit like it has no bones in it. Which way is it facing? and where is his elbow? It also looks a little big around? It might just look like that because the cybernetic is so different. Lastly, his left hand looks a little disproportional to the rest of his body.
Hey, Artox. One thing you may want to think about is whether or not the viewer could TELL that the anatomy is supposed to be wrong if it wasn't explained to him. Also, the human hand is WAY too big. Have you practiced very much anatomy drawing (like, from a book of actual people, or something like Anatomy for the Artist)? If you have, just keep on doing it. It's always a good idea. If you want to see how somebody DRAWS really good anatomy, try to find a comic drawn by Bryan Hitch or Greg Land...Barnes & Noble or Borders should have some compilations of JLA, the Ultimates (both Hitch), or Nightwing (Land). Hope that helps.
some sections on his body seem flat, like his waist and his pistol.
10x for the comments guys. I'll try redrawing this and reposting it soon.