I just downloaded it and gave it a runthrough. It is very very dark. I don't like running around with my flashlight on. It's a shame it's so dark because you obviously put effort into decaling the walls and making the ceilings and walls interesting. Unfortunately 90% your effort goes to waste because I can't see the majority of your level. The only place that I thought was well lit enough was the little corner with the shotgun and the smoke.
Your next problem is connectivity. The map doesn't present you with enough choices for routes. For example, if you're running down towards the swamp area there's no other way out. Once you get down there either route you take (the sewer pipe or the long thin tunnel) just loops you back into that very room. And the only way out is back up into the area with the containers and standing spot light. The rest of the map follows a similar circuitousness, although it's not quite as bad as the cul de sac you've got going on in the lower part of your level. The only really good part about your layout is the section where you can drop from the upper level down into the aforementioned cul de sac. It offers the only variety in terms of layout.
Here are some suggestions to improve the layout, just off the top of my head:
1. Connect the dark combine room with all the pipes to the room with the shotgun and the cold effects coming out of the grate. By doing this you will eliminated two dead ends and at least give people the option of approaching the central area from a different angle.
2. Incorporate more Z-axis mobility like the area where you drop down into the water. There are plenty of areas where you have two rooms on top of one another. Why not add a maintainance ladder connecting the two rooms? For example... connect the swamp room with the room above it.
3. Perhaps you could put a teleporter in that flooded room and have it take you back to the combine room with all the pipes. Make it a 1 way teleport.
The performance of the map is fine, it runs great on my computer, because it's such a small map. That being said, you can definitely add some more props_physics, as this map doesn't really have many things you can toss around.
The env_glows you've got going on are waaay to bright. When I look down some of your upper hallways I feel like a deer standing on a foggy highway with giant trucks bearing down on me. The glow you've got going on with the standing spotlight in the room with the containers is just ridiculous! It's like I'm staring at God. Tone those down and the effect will look much better. That being said your spotlight effects look great.
I appreciate the fact that you included an env_soundscape. I liked it, definitely helped create atmosphere in the level.
I have other comments on improving the way particular parts look. I have a bunch of screenshots taken to illustrate my points. If you startup a forum thread I'd be happy to give you feedback, kind of like I did here:
http://www.snarkpit.net/forums.php?forum=2&topic=4641&chap=2&findpost=newest#newposts
Anyway, good start. The only problems I saw are easily remedied by adding more lights and improving the connectivity. Hopefully you will take my suggestions into consideration and make some big changes for your next beta. I think this map has the potential to be a tight and fun map for 4-8 people.
