Kargeff, it's his first map...dont forget that!
okay, let's see:
First of all, the lightning: the whole map is much too bright! But I assume, that you didnt add any light-entities at all...so thats what you should do next.
Secondly, the mountains: To be able to create realistic mountains, you need to get familiar to vertex manipulation! This tool is the key to good lookin outdoor environment!
look at this pic, its from one of my esf maps(nearly all brushes in this pic are edited with the vertex manipulation tool!!)
So, all in all it's not such a bad map,
considering it's your first one!!!