The effects around the sniper seem misplaced, i'd try to re-orient that to in front of the barrel, but the effects on the spartan are pretty nice. And the size is awkward, 500x150 is usually nice, anything with a widescreen ratio looks a lot better. But still, decent work none-the-less.
Also, I believe that the text pops out a little too much. I would darken the color of it a bit to fit the overall color scheme of the pic. And yea make it a little smaller and widescreen it actually makes it look A LOT better. Nice work though...