Welcome to the forums man!
First, I'd like to say you seem really talented ( far more than me I might add
). So if anything I say doesn't really bother you, just ignore me. This is just my opinion.
I'd really like to focus on what fil was focusing on, about the curtain like parts of the rock on the left side of the mountain face. It would do you well to make more defineable faces on the cliff as well. Plus, some details and cracks and such like that also will work wonders for you.
Dithering:Dithering is one of my more favorite forms of shading things and can be one of the most effective in some places and others for texturing on a piece. But it seems to be overdone on this piece and made things seem smooth in some places they shouldn't. Adarias has some really nice rock references, I'll link them to you when I find them.
Overall, this was an excellent piece my friend.