The design elements seem to be working okay right now, to help you in the design you could think about what type of character build it would be to enforce your design choices.
I'd like to see his feet as an art director if it is character art. On his left arm (our right) the elbow functionality seems to be glossed over .
The perspective on the assault rifle and hands distracts me from the overall piece the most and the perspective of the contours on the amour overall could use some perspective correction
But the good news is since it is line work still you can fix these things all day long at this stage. 
Just want to help and not be too harsh. Things like this are really fun to paint when you get right down to it. Good luck and let me know if you have any questions.
