I just ran through your map. The general layout is promising. There is decent room to maneuver. I like the mine shaft in the second stage. I think you could afford to have larger doorways for a lot of buildings. The second point of the last stage seems to have a lot of passage ways around it; perhaps too many.
You are going to want to stay away from the HL2 textures.
Aesthetically, your map is developing. I think your biggest problem with appearance is precision. You might want to run through and make a list of the little things you find. I'll create a list of things I can remember noticing:
Stage 1, Blu Spawn: Purple light on the floor
Stage 1, Blu Spawn: Small slit you can see through between the left and center exits upstairs
Stage 1, Point A: Boiler with the gold in it sticks through the roof
Stage 1, Point A: Mine cart track on the right don't line up with the tunnel exit
Stage 2, Point A: Light bulb prop sticking through the roof of the shack by the point
Stage 2, Point A: Holes in the displacements underneath the point
Stage 2, Point B: Those trails leading to the point aren't connected
example
Stage 3, Point A: The end of your conveyor belts (nice job making them, BTW) is going the wrong way
I remember there were some oddly lit props. You might want to use some
info_lighting entities.
Also, building interiors could generally use a little bit of love; especially spawn rooms.
Your map has promise. Your layout is strong. I can't make much of a prediction to how it will play, but it seems to me that it will have a primarily Dustbowl feeling with a little Badwater mixed in. Good luck, the map is coming along nicely.
