Suggestions/Observations:
1) I like the layout quite a bit. Nice connectivity. Detailing is also cool. Nice pipework. Maybe break up that one cracked floor spot a bit more, or have a couple of loose bits on top and/or tilted at an angle?
2) I agree with Psyche911 re: the lighting--it certainly doesn't look bad IMO, but there are parts that look really, really nice and other parts that look sort of meh and bland. I'd be hesitant about adding color (or at least too much color) to this map, but yeah, a bit more contrast in spots...or something.
3) HOM/visible caulk under a light near the RG
4) Lots of sparklies/t-junction errors around bevel caps (e.g. at the top of jumppads) that should be cleaned up).
5) I like the way to get the Quad via teleporter. Right now you can also rocket jump up to the corner of the catwalk to get it, and you can also jump to the sloped brick directly underneath and the crouch, go the the back, and rocket jump up from there. It seems like you can *almost* get up to it with a regular jump from there. How about making that possible? You would still be begging for a rocket enema as you screwed around crouching and creeping along the sloped brick to get under/back there, so I don't think it would be too easy...
6) I love the jumppads/trench to the MH. Kickass.
7) Where's the camera that we're seeing the LG through? I don't see any camera down there...
8) Is there only snow/ice in that one spot (underneath the hole in the high corner)? Consider using a patchmesh for the snow and/or shadeangle in the shader--right now it looks blocky and assy. I'd also *really* like to see more areas of snow in here--it would really sell the whole COLD feeling that you're shooting for. And where the heck are the icicles?!? Needs icicles...maybe some big patch mesh ones in a few tucked-away corners where it wouldn't slam the tris too bad, and then some smaller alpha-channel ones hanging from pipes and edges in various spots? A couple more ceiling holes in spots would be cool too...
[Edit: I second the suggestion below for a YA. Also, how about something to mark that tele-dest? Some sort of little apparatus, or a (clipped-off) gap/crack in the wall or floor, or at least a scorch mark or something?]
I beat the internet; the end guy is hard.