Everything works well for me except the shadow around the guy and the gun. It seems very non-organic. I'd blur it a bit and move it in towards the guy.. or do some sort of perspective transform on it so that it simulates being on a flat wall (what I think you were trying to do with it) better. I REALLY like the font choice/texture/placement.
Elaborating on what Cosmic mentioned, When using drop shadows, drop them down immediately to something like 30%, then adjust from there according to the nature of the rest of the piece, colors, etc. I think PS's default drop shadow is about 70%, and its WAY too thick. 30% or so gives a fairly natural shadow (40% if you're feeling frisky). Try that out if ya get a chance. (and if you're not using PS.. well Im not familiar with GIMP, but the principles should be the same I'd 'spose).
It's the same in GIMP, assuming you've jumped through the ridiculous hoops necessary to get the layer effects plugin to work properly (totally worth it). However, I prefer a darker shadow than LIGHTS, apparently. At least for small distance shadows (1-10 px) If you're going as far out as you have, though, I'd blur it and make it lighter, as LIGHTS suggests.