This was really unique, I loved the brushes and the way you used the textures. The second point you mentioned about "Use enemy combinations, geometry, weapons and environmental hazards to create encounters with different combat problems." particularly about geometry and environmental hazards is in my opinion the thing that makes great Quake or at least that's what I love most so I'm glad you approached it that way. I would have loved some more exploring or interconnected design for a choice of how to progress but that may not have been the goal so that's just my taste.
I have a small bug to report, I was a little too far to one side when falling down the chute at the end and fell out of the map.