I like the background though I definitely think you could add some hue shifting and bring in some warm yellow sunlight.
I don't like the most foreground bricks though, I think you should explore some larger and more interesting structural designs, perhaps pillars and bricked over archways etc, if ur going to fill that much screen space. You should probably darken it off into some kind of shadow area if bottom leads to nothing but unplayable space, while the top line of it should have some more sunlight hitting it to stand out.
I don't like the barbed wire. It's too black, too straight and just seems to conflict with scenes perspective somehow.
Perhaps use it sparingly and make it all broken and twirly sections here and there with bent posts and stuff to make the place look run down.
I also think you need do something with how the background buildings connect to the ground, add some trees or cars or something.
try varying the colour of some buildings a touch.
As mentioned please don't mix resolutions like you've done on foreground character that looks horrible.