Hey pal, it seems you've come a long way since you first show me this. For starters his srmor seems to be made of clay rather than metal, it is very round and not shiny enough. His arms seem to in a very tense position and they are a little short, His feet seem to be a little big and look like two potatoes. The cape looks like it is made of cardboard. Like you said before he is very monochrmatic and therefore very dull, try using hue shifting and reshape the armor. Well anyways I hope this help I'll leave you with this edit I made for you hope it helps.
Cheers!

P.S: I didn't shade the cape I just redesign it.