Right, here goes.
0.
Nice floor texture. The trim is nice. The walls and ceiling are terrible.
1.
Pointless dark corridor. Nice staircase; good banisters.
2.
Terrible face splitting there, making the lighting jagged. The best thing to do in this instance would probably be to move that wall a tiny bit away from the staircase. Alternatively, you could tie the entire staircase to a func_wall, but that might be a bad idea with such a large piece of architecture.
3.
Ceiling's a let-down again here. The walls lack any detail.
4.
Much better. Feels a lot like a car park under here. Better ceiling, too.
5.
Weird lighting on the strange box thing around the map. I'd suggest you use sky instead. Look at the Environment tutorial. That building with the glass is rather nice, but the bushes are a bit square.
6.
Nice, but you can fall off the edge of the map!
7.
The textures on the bottom of that look nasty. Rotate them using Texture Application mode. If you don't know how, read the tutorial on it.
8.
My favourite bit.