the map is too angular and random,
the ceilings are all too low and why adding surroundings (like the terrain outside) when theres no chance to take a look at it?
Please also consider that lighting is as important as the architecture, but you rather start with the layout, before thinking about what lights you place in your map, put a mood in your map.
We humans differ from robots with our feelings, and we can put feelings into a level, which others can feel who plays the level and puts effort into "feeling" the map.
Nieb did for example very good in putting a scary emotion into the map hallo
or in nevil_c
but thats more about design then layout.
make your map "flowing", (not to mix with floating), flowing means that you can run in the map easily without getting stuck on a stupid crate or bar.
try to play on a good ctf map, eg reissen or forge, you will realize very fast that there is nothing placed random and you can navigate smoothly and fast through the level.
every addition or substraction in your level can make the level either good or worse. keep that in mind.