Your shoulder piece's diffuse is too saturated and bright. Try lowering it. The normals on his skin in some parts don't help the form of the low poly. Lower the intensity of your normals, or put it in a game engine. (concept's really good!)
Any reason he's not asymmetrical like in the concept? (Armour parts I mean) Also it would tickle me if you can post a version with flat grey diffuse textures, I'm curious about the normals. Cool stuff!