The bg is really good, I like it. Has a "TEH GATES OF HELL ARE OPENING!!!" feel, looks really nice.
Minor: Make the light source more apparent, it's placed well and everything, it just needs to pop out a bit more. (I'm talking about the yellow spot on the upper right, if that was an unintentional light source, then lie to me and make it better (: )
Major: Lose the 1px stroke on the focal. It ruins the blending completely and makes it seem like you just slapped him on. Try blending him in some more to make it all tie in and look like he belongs in the sig. Also, to improve blending, add some foreground effects. Put some of that red blood looking stuff on the left over the guy to blend him in some more.
Overall, it isn't half bad. It just needs some retouching with the basics in mind.
Low to Solid Novice.