I like it ! the lighting work on the shield is very well done. For me the only thing weird is the head, it's like it not belong to the same universe of the rest, too light maybe I don't know. You should try to do it more darker I think I'm not good on critique, sorry ^-^
In my opinion it lacks a bit of punch, maybe needs more contrast, the armor is looking a little dull. I like the design of it though, on the whole he looks pretty cool. Here are some thoughts on the lighting, most of it is just getting the armor to pop a little more, particularly the teeth on the torso, they look great when a little more prominent. Anyway there's two different versions of the lighting in this paintover.