If you design your map well, you won't need detail brushes to have fast vis times. If you design it very poorly (or use a crappy editor), even detail brushes won't save your vis time. *cough*twilight*cough*
As for the map, I just took a look at it. It's not bad for a first shot, but like most first maps, it should really be chalked up as experience and left alone so you can work on new, better maps.
Some things to avoid:
- Ladders to flags / as the only entrance to a base. Ladders are far to easy to defend as the attacker almost always has his back to the defender. In this map, it would be far to easy for somebody to just sit at the top of a ladder and spray, making it impossible for an attacker to come up the ladder. There should always be multiple, easily accessable, able-to-reach-blindfolded-while-running-backwards paths to the flag. This keeps the gameplay flowing and makes games more interesting.
- Box maps. Box maps are boring. We have hundreds of them already. Even though they may be "different", they all tend to play about the same. Instead of making a big box and putting stuff in it, plot out an actual map layout. I'd actually suggest looking at Counter-Strike Source maps for inspiration. Take a look at some of the top-down views here:
http://www.lfserwis.pl/infopage.php?id=110- Overlapped brushes. It's OK to overlap brushes in some cases, but not if you have two different brushes with faces on the same plane. The end result is messy. Sometimes you just see one of the textures. Sometimes it tries to draw both of them and you get z-fighting going on where 2 different surfaces flicker into view.
- Unlit / Overlit areas. Under the base there's no lighting, while the area by the flag has tons of light and is super bright. Get a nice balance of light/shadows, but don't make areas too bright or dark. It looks bad.
Also, grab that bsp build15 pack. I'm pretty sure you compiled this with the old one.