I'm very canny concerning praise, so I will quickly get over to the suggestions part.
1st picture: Looks ok. Especially those rounded curves, hopefully not at the cost of r_speeds. The lower floor, with the corpse on it, needs more detail. Some blood traces or so, trashcans, benches etc. And you should put something between the grate and the floor on the upper level, just a single sill.
2nd picture: Boring! There's nothing to look at, yet. Put some signs or ventilation shafts there. And make those lights func_walls, they obviously split the walls and add those nasty edges.
3rd picture: Also a bit empty except for those boxes and barrels. I don't know what it's supposed to be, but if it's a storehouse, you could put some kind of transportsystem for the crates there. An unloading point for trucks might be look good too, or just a big freight elevator.
4th picture: Empty too. And as you already said, way too dark. You could boulder those empty walls with pipes spitting out dirty waste.
The bridge looks moveable. Why? Put a train track there which crosses the bridge to make the purpose for that movable bridge more obvious. The banister looks bit plain too, just add some pillars to it.
For the lighting: I think all the pictures are a bit too dark, make the levels brighter. If you still want some darkness, you could add some broken lights at critical points.
Ok, I hope all this didn't sound too negative, it's not meant to do.
If almost never say good things about the work of other, unless it is really good. Just don't take it personal.
Anyway those pictures look like a good start, keep working on them and the result will be also good.
Just repair it!