Looks nice, but 2 things:
1: I think that 3d backgrounds (buildings in the distance) should be placed in a fake skybox or something outside the map instead of being a part of the map.
2: It looks like you don't put so much work on the architectural work of the walls, ceilings, etc. Something you can do is try to add as much detail where you can, extrude edges, make curved walls with different shapes, use arches, carve out parts etc. It will make the levels look more realistic
Here is a little example i found on google image

It's scifi but still.
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