Composition is great... Sky is a little light, but that is necessary to get the soldier at proper exposure. This image is why fill flash was invented. This would be a 10 if there were some light on his face. As it is, my eye drifts to the end of the weapon, when it should be on the guys face. Fill flash would have brightened up his face and made it the ceter point of the image.
The face here is very dark, which is an interesting choice as it makes this subject appear like an Everyman type of figure. However, the detail that IS there is very interesting, and I find myself craving more. Perhaps either darker or lighter would work? It might be fun to experiment. Very nice composition here; the neg space invites my thoughts to extend to the world around this subject.