Hi man:
First would be, dont save as jpg! it ruins the exactitud of pixels, and damages the capacity we may have to critique it.
Second, i think the biggest concern is that you used too much of the same colour, not really separating the areas by tone and depth, they all look as if the lightsource is casted right upon them, the design is nice overall, but could use more work.
It also looks like you AAed the gun to the white background, wich doesnt really make sense.
Start by posting the picture in a loseless format, and weŽll take it from there.
-Krut.
