Observations/Suggestions:
I agree with some of hemostick's comments. Yeah, light fixtures are good.

The lightcount is high in spots, but it looks like nearly all of them are non-shadow-casting, which is why performance doesn't suffer. I really think you could do much better on the lighting with a bit more work and fussing-with. More color would probably help, but I think a bit less evenness and more shadows would too. Easier said than done, I know, especially with a map that's large and interconnected. For the love of God, please do something with the shadow-casting light directly under the RA/RL room (on the lowest level) somehow, or make a fixture for it, or something. The player's shadow is really obvious there, due to the placement of the center, and the lack of fixture/source makes it really bleh.
Your portals are busticated on one side of the giant curved hallway o' doom with nothing in it. One of the V-shaped combos doesn't touch the wall at the point of the V...
Layout. Many areas feel really big and open. And plain. You could make some of these (like the aforementioned big curvy corridor) a lot more interesting by throwing in some pillars or level variation or wall variation or something to break them up a bit more. Doesn't have to be super high detail stuff--just some simple square pillars with a nice texture on them would work. I really like the level-over-level stuff in the RA/RL room--this combined with numerous bouncepads will make for some fun gameplay in that room.
Dead ends suck. Even nice dark ones where you can camp.

That one, the one with GL, and the two weird drop-down shafts to nowhere from RL/RA area all need to be either done away with, or connected to something, somehow. I also strongly think that that RL/RA area needs another connection of some kind with the rest of the map. I didn't find it for quite a while, and then took a few seconds to figure out how to get back out, while jumping down dead-end shafts and cursing. How about a jumppad that shoots you up and over the whole map through a tube or something and drops you down on the bridge in front of LG? Or just another tele, if that sounds too crazy.
This is a good start, but needs more lovin', IMO, especially lighting/detailing.
Edit: Damn. Looking at this has me in a Q4-y mood again. Maybe I'll start working on something...
I beat the internet; the end guy is hard.