ok lets analyze this
a bit.
you used many smaller water blocks to act as one, which causes alot of uneeded faces between them
http://img74.imageshack.us/img74/6715/12zk.jpg
you made the whole underwater ground func_wall? wtf?!
http://img74.imageshack.us/img74/8647/20rw.jpg
a func_wall is NOT ment to be used for stuff like this. Also, entities (func_wall in this case) do NOT block VIS, thus you can "see" through them. In this case, you get alot of uneeded faces since VIS looks through the func_wall and you can "see" below the map
http://img192.imageshack.us/img192/2760/39co.jpg
the same goes for the hill top thingies, func_walls arent that bad at that spot, BUT close the holes below them, else you have a ****load of uneeded faces
http://img192.imageshack.us/img192/4674/41zg.jpg
there is no lightning in your map. very bad.
use NULL textures for unseen surfaces
learn how to effectively scale textures to reduce r_speeds.
make use of the grid, use a snap of 8 or so for most of the stuff, makes it easier for the mapper to keep the overview.
read the stuff i mentioned before.
so, even though the overall layout looks fine to me, and i think it could be a fun map to play, i give it a 1/10 because of the enormous lack of technical understanding resulting in almost 5k wpoly ...