Hey guys, thanks for the reply. I've reduced the fog intensity, now it has a lot less impact on the scene I think. There are some global postprocess effects like DOF or bloom, and lighting is tweaked a little. On the screenshots you can see fog particles and ventilation meshes which also makes the corridor segments look less square and blocky. I will probably try to tweak the ventilation more (since now it has that green thing coming out from it ), and also I want to add more details there, like wires hanging from the ceiling, or some organic parts. Just want to precise the general mood of the environment first.
Edit: I've just noticed that after resizing the screenshot from the original size (2880 x 1800) some parts of it looks like they are almost black, while they are pretty fine in game (they are dark, but you can still see the geometry). Hmmm...