It doesn't look professional at all, unfortunately. If you want to use block-like terrain that looks manmade, use a metallic texture; even then they should be more sophisticated than two polygons being a rectangle.
It also lacks a lot of scenery, even though you may purposely have wanted to achieve some sort of effect that way. But at least give it crates, barrels, sandbags... that kind of good stuff, and maybe support.BMPs or col#.BMPs just to make it more aesthetically pleasing.
The atmosphere, man. Convey a 1337 atmosphere. The gray BG ultimately seals in its medoicrity. This just looks boring, to be honest.
(Yes, I realize how mean this post sounds, lol, but I'm just trying to be honest and straight-to-the-point. I'm sure this could be a great map, if tweaked... heavily)