First off you might want to work on a darker background, white is kind of bleh and makes it hard to see highlights.
Hopefully I haven't butchered what you were going for too much and you can see what I was sort of trying to do. Yours looked like he was falling over backwards and the perspective was kind of odd, I tried to fix the perspective but the side-view might not be what you were going for. I left your head pretty much the way it was, I actually really dig what you did with the mask.
Basically what I did in the eidt was mess around with anatomy a bit (the arm is completely off and blobby in my edit but I think the size proportions are okay) and edit your coloring a bit. Your coloring was a bit unclear and could have been cleaned up and there were al ot of very similar values, which I hope I cleared up. You might not want the boots and the shoulder/chest armor, I don't really know why I threw those in. I guess I wanted to break the brownish monotony a bit. I also left out the energy pack on his back, I wasn't really sure about how I would go about adding it in with the colors I had without making it look too odd and this was kind of a rushed edit. Sorry about that.
It's not really a great edit but what I hope gets across is: cleaner coloring, more contrasty hue shifts, better readability, anatomy, less colors.
Hope this helps and isn't completely wrong style-wise.
