This looks interesting, but I’d pay attention to a few things-
most importantly, specularity. Without a spec map, everything looks like it is made of wax. This is especially important for surfaces like stone and concrete, which have a lot of flecks of different materials in them, and absolutely need a spec map to look right. I would argue that that’s more important than a normal map.
Second, your decision to place what looks like concrete blocks on the ceiling seems strange to me, concrete is very heavy and doesn’t have great flex strength- it’s good for support, since it can take compression well, which is why you generally see it as floors and walls, but not ceilings.
Third, take a look around the edges of the room you’re in right now, especially where the walls meet the floor and ceiling. Generally there’s a small buffer between the two, rather than a sharp edge- without this, a room looks very bleak and empty. You’d be surprised at the difference it makes.
Fourth, watch where your textures line up- the outcropping wall clips the brick texture partway through the bricks, which seems odd- I doubt anyone would want to cut the bricks to fit them in that space, and if they did there would probably be a seam visible between the wall and the brick. I recommend shifting and resizing your texture so the seams between the bricks line up properly with any intersecting objects. Same goes for the grid pattern on your first screenshot. Making textures line up is a huge factor in making a scene believable.
Finally, I’d bake in some Ambient Occlusion (or use a shader, if your target computers have enough processing power). As light bounces around corners it degrades, which causes corners to be darker than large flat areas. Ambient Occlusion really adds a sense of depth and solidity to your scene, and has a significant impact on the player’s sense of how “real” the place is.
I know I’ve said a lot of things to fix, but that certainly doesn’t mean your project is bad. I’m curious where this is going, and you’re doing a great job so far.