My quick two cents
I really like this map. I feel like it's got a lot of potential to become one of those maps synonymous with Garry's Mod, with maps such as bigcity, fork, valley, etc. I'd love to use this for my server's default map if it weren't for two things, which I'll describe below:


The optimization. It's... not that good. I get an average of 40-50 FPS on this map, which isn't bad. But that's the average. It dips to the 20s zone when overlooking the entire map, and that's with detaildist disabled, no grass. (660TI, Quad-core CPU @ 3.4GHz. MCore enabled in gmod.)

The lake's depth. The one near the center of the map just to be clear. Underwater building, creatures, etc are a common thing in my server's community, and the lake isn't exactly very deep. It works for boats, but not for underwater bases, creatures, submarines, etc. The air space is absolutely massive right now (to the point the map goes out of render distance if you go up high enough), and I think it can take a tiny hit if it means a deeper lake.


A small map addition: Have you played Half-Life 1? A pipe connecting one side of the dam to the other, optionally with an openable/closable water gate in the pipe. It just seems like a cool addition that could make the map feel more alive and have some more depth.

A small bit of support for an addon: There's an addon called StormFox - Environment Mod which adds a realtime lighting system, day/night cycle, and weather/wind to the game. It controls visual functions with six map entities, right now your map has four of these six things. The only two which are not present are the light_environment and env_tonemap_controller entities.