Interesting layout, but in my opinion the external areas are too bluish, even more after your update. You should set the light_environment in tune with that skybox. In this Valve viki page you can find the suggested settings for each skybox: https://developer.valvesoftware.com/wiki/Sky_List
About visual aspects, those metal handrails props are acceptable for the external area, but are a little "heavy" in the internal corridors and stairways. You should plan to replace them with lighter ones, handmade by thin metal textured brushes, turned to func_detail.
Even the interior of Atlantic building is too blue, in my opinion, and there is too contrast with the pink/orange lighting at second floor. How can fluorescent tubes give a light of that colour?
At last, the map must be cubemapped, to get the right reflections on glasses and models.
However, being your first HL2dm map, it's surely a good work, even if perfectible. Keep it up.