Thanks for the feedback, everyone. And yes, it's raining in that last shot.
As far as the spotlight suggestion, I was thinking about making Red and Blue (respective to bases) spotlights outside each base aiming up at the base. I could see that becoming a horrible disaster, however, so I'll have to investigate it carefully.
I worry a bit about the map being too dark overall - I think I'll lighten it up just a tad, but I still want the rainy overcast theme. And thanks, everyone, for the comments about the exterior. I think that the wall textures I'm using outside right now work very well, and I'll probably keep them.
Since I feel very well recieved by the community here, I'll post some more shots:
Water entrance looking at the base
Roof looking towards water entrance
First floor near spawn
Second floor
Rough ovearhead of the map layout
And now I'm going to break a norm and show the ugliest parts of my map right now:
Flagroom Still figuring out what to do with the walls
Second floor of spawn 1 Still figuring out detail and lighting
On the way from the roof to the flagroom again Working on how to make the end of the tunnel pretty.