I really like the map, some great architecture and the lighting is perfectly dramatic if you ask me - works to the architecture's advantage nicely. That said, there are certainly improvements to be made, I'll point out a few flaws here...
You use this texture a bit too much - its a good all purpose texture but I think you have gone to extremes here. I think you should slide a few different concrete textures in for variations sake.
Nice skylight, but you hide it behind repetitive texturing. Highlight your features such as those light fixtures with different textures.
I think the walkways are maybe a little too thin, perhaps widen them a little?
These metal bits look pretty crappy and pointless, perhaps make something that looks more structural sound? Take a look at these pillars in Forsaken - the have variation in them to provide interest, yet still look sturdy.
Perhaps aim for something similar - the thin points in your pillar look weak and should have something more than those little metal bars to hold them up.
There is an awful lot of texture layering on a flat wall here, perhaps provide some architectural depth to it? You could have an indented alcove/ledge at a similar height to the lower ledges or something?
The doorway trim has depth to it at the top yet is flush at the sides - you should maybe pick one and make it consistant. I'd be inclined to suggest keeping it flush to stop players getting snagged.
Players can barely see anything below because of this wall. I reckon it would be better to remove this and keep the upper floor exposed, the same as on the opposite side with the windows.
You may want to consider linking your pillars with the inside wall somehow to break up the ceiling a little. It could provide potential for interesting light fixtures too, since the little green squares are a little lacking.
Watch your texture alignment, its off in a few places. If you are using a texture extensively, that is non direction dependant like this one, you can sort your alignment really easily for the most part by using hammer's texture replacement tool. Just open the texture tool, set the mode to "select", press "replace" and select the texture you want to select in the left box. Before you press continue or whatever ensure you have checked the "do not replace textures" box. Now you will have all the faces with that texture selected, so you can easily align them all "to world", set them to the same scale, and centre them or whatever.
Are you doing something with this wall? Looks awfully boring and temporary.
All of these could be linked up with another room behind your boring wall, and you could perhaps not so much make it another room, but an extension of the existing main area.