I finally got a bit of breathing room over the holidays and ran around this for a while--it's looking really good! It may be slightly dark for my tastes, but I took a look at your lightcount, and I don't know that I would push it much more in a DM map...
A few observations/suggestions:
1. When you drop through the bars heading toward LG, it's pretty easy to touch the top of the teleporter trigger unintentionally--how about lowering that down?
2. There are a few places in the map (most notably in that same RA/LG area) where it's very difficult or impossible to jump down to a lower level without taking falling damage. That sorta sucks.

You should always be able to move around a map easily without taking damage, IMO (unless it's an obviously big drop--these are close enough that it looks like it might not hurt you). I don't know what would be involved in fixing this...it all depends on what approach you would want to take. Options include ledges/pillars here and there, or major reworking (e.g. lowering/raising floors and that sort of

stuff). You could always put common/cushion on the floor, but IIRC that gets rid of footstep sounds too, which would be bad.
3. The map seems pretty quiet everywhere--you always have to be careful adding ambient sounds, since you don't want to drown out audio cues of other players moving around too much, but I think it would be cool to hear maybe some wind noise up near the top or near windows/openings? An occasional bubble from the lava? Hums from the teles? Burning noises from the torches?
4. How about some markers for tele dests? Just a burned/discolored place on the floor would work...
5. Finally, this is sort of a wacky one, but I always love vertical in maps, and that one hallway, although it's prettier now, is still a bit bare and sorta eh. How about a drop-through hole over RA that can be accessed via that hallway? It would add a fun bit of extra connectivity, and you could make it take a trick/difficult jump to access. I *think* you could do it without hosing your current portaling...
Hope this helps.