A platform goes *up* when the first shambler arrives, and goes down when he dies... So I'm not sure what you mean. 

I just downloaded the demo - where do I put it? I have it in ID1 but when I try to watch it tells me I don't have the .wav file. 

I couldn't get the gold key after killing everything because the passage was still blocked by bars - I assumed I was supposed to be stood on top of the platform so that I could jump through the windows, but they had clip brushes to block that. What's the proper progression there? Is it one of the shootable switches others mentioned that were hard to see (?).

Also, did you make the blue base textures yourself? Not bad, but they need a bit more work, IMHO, the photoshop filters were very visible. Maybe a few partially transparent dirt textures overlaid and selectively erased would look good. 

I'm not sure how you activated the shambler ambush without being in the room where the gold key appears. You're supposed to take out the first shambler from the computer room, and then be ambushed by the second. I'm pretty sure the bars are drawn after you acquire the gold key.
The textures are all taken from Starship 1 and Starship 2. I love that texture set even if it's old and outdated. It adds a cool old skool touch to things. 

Was fun to play anyway, and at least I know I didn't miss anything important. Haven't seen that texture set before, I don't think.