This is one GIANT map
feedback time:
There are a lot of very large hallways, but they feel kind of empty & slightly maze-like. Try adding more details like ventilation & pipes overhead. Maybe some support beams etc. Half-Life 1 comes to mind where there were colored pipes going from the central ignition chamber to all the separate areas. Adding stuff like that grounds you in the world and gives you a trail to follow and something to communicate to your teammates.
Also try to break up very long straight sections. Put a forklift in there, some crates or slant the wallway up/down or curve it a bit. That will help take away the DOOM style level design.
Lighting wise, try to strategically think of light as a way to guide the player, removing light from dead ends & adding light near a doorway or stairs.
The boring way to light a room is to just add ceiling lights and have uniform lighting all over the place. Try to think of certain things / setpieces you want to highlight. A generic design rule when distributing light: try to have the play area lit up 75%, the walls 50%, the ceiling 25% and setpieces & escape routes 100%.
Visually also try to place "filler" lights as a way to simulate radiosity aka bounced light. UDK Lightmass used to do this automatically, but tripwire has replaced the lighting system and now you have to do it manually, old school UT3 UDK days
There are also some sections of your map that are completely pitch black. So when your flashlight runs out, you can't see anything. That can be a deliberate gameplay choice, but I would add some very slight fog so that you can at least see some silhouettes of the enemies around you.
( In general, Left 4 Dead 2 is a fantastic showcase for great level design. )
Zed spawn wise, because of the long hallways without any nooks or crannies, zeds need to walk a long straight path towards you. This can lead to an entire wave just walking in one long line towards you. KF2 usually despawns zeds and respawns them in a spawnzone nearby, but cannot do this when you see the zed from a mile away. (this is where the crooked & broken up gameplay wise hallways would help a lot)
Some small bits:
There is a texture missing on the ceiling at the base of one of the stairs.
Some weapons and grenades in the racks are missing textures.
I really like the giant submarine. I would take that element and treat it like the central hub of your map.
Phew... that was a mouthful
I'm interested in seeing how this map develops.
Technical stuff: Yes precomputed visibility is a b*tch, it takes 4-5 hours to do a full rebuild on my map with my computer, and I was forced to dramatically reduce my overclock on my CPU as it fully stresses my CPU to the max beyond anything else. I usually build it overnight while I'm sleeping for public releases, but when testing with friends I don't bother with it.
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