When you say it's not that dark it is probably because you have your brightness settings very high ingame(?), however on my settings (r_gamma 1.2) it is just too dark. These images were also brightened in photoshop:



It's obvious you were going for a night theme and I noticed you used a soft blueish ambient light (which is a good thing) but without any additional pointlights (e.g. lightposts, lamps) it's very hard to see anything in front of you. Nonetheless the structural part of the map seems fine, some pretty nice rocks and terrain. The layout seems okay too, good use of heights and cover.
I don't know if you're still open to suggestions and of course the choice is yours but I really recommend adding some light entitys to get better contrast and make it easier on the eyes.