Man, this is awesome...I just think it needs one thing to put it over the top! A little atmospheric perspective towards the background would really help give it more depth. Other than that I wouldn't change a think. Love the way you rendered the rocks, and those clouds are gorgeous.
Cool man, no worries! I've been watching a lot of concept art tutorials lately and atmospheric perspective is a basically the main tool they use to show depth, other than standard perspective. If you just de-saturate some of the parts of the cliffs that are further away that would really help. Like I said, other than that its an amazing piece!