Dark and nice looking, thou you should have worked some more on the two characters, just as puppychow16 said. A standard Photoshop filter is a no-no =/
The concept is really cool thou, not seen any dark Trigun papers before =)

I like a nice dark wall like this, the lighting on the cross has
this lone or fading feel to it.
Lost and forgoten life of a character, hero, is what I get from this
Hope it is the intent of it.
Any way Great work! , seriously.

Ya know, some people will like the characters and some people wont, I feel like maybe instead of making them the same shade of red you could have made them go from brighter to darker as if the cross was emitting some sort of light on them, they could have been colored normally or in the red, though I think the red would be cooler. The basic concept is pretty good, and I think you did a good job with the cross.