I love this concept! Proportions all look great. I'm just wondering where his hands are, though. Tucked into his pants or his jacket pockets? If the latter, the right side looks fine but the left makes his arm look a little short. If the former, I'd expect to see a little more bulge in the fabric of his pants. I really dig the pin and the mask, though! Nice touches!
I love the rendering of the cloth, face and all the attire, however the grenades stand out as not wrapping the form of the figure. Part of it is how all three are facing about the same direction, their lack of size difference (shrinking in the distance) and the shadows do not show depth of field (a soft envelope of light towards center would help, along with sharp shadow blocks for where the coat is in front possibly. The direction of the duct tape is also a bit undefined. This is all really nitpicky though, The painting looks fantastic!