The overall design is very good. I do get some pretty big slowdowns on my 6800 Ultra, though - drops down into the high teens at 1600x1200, no AA, 4x AF especially in the initial outdoor area.
My biggest complaint relates to enemy spawning in the first part. Perhaps there's a way to incorporate a 1-2 second delay from the time the marine picks up the weapon. Or maybe move the spawn location away from the weapons. The cacodemons show up and I'm down like 10 health before I've had a chance to get a shot off.
Excellent map otherwise.