MEH, its not bad, but the grunge is a little too random and splotchy. doesn't really flow. Could use some more color.
Also the lighting by his face looks bad. you should add a gaussian blur to it and maybe add some color to it.
I was following a tutorial, and it called for lighting using a round brush with low opacity. I used a bunch of applied images though, so I would have to start all over if I wanted to fix it. Yeah, I tryed to fix the lighting around his face, but I just didn't feel like starting over to fix it.
It looked a lot better on the sig in the tutorial.
Thanks for the comments.