As far as the cliff sculpt goes, the rock forms are looking a bit too soft and rounded. The sculpt itself feels more cartoony right now, while the diffuse and alpha treatments suggest you want to go for a more realistic feel. You may also want to revisit the crevices between the rocks, some of them have weird pinching…
I agree with khalamea. You may want to work a little on the diffuse and add some color variation. Right now it looks like an awesome mound of chocolate which COULD be good, but I don't think that is what is intended with this :P Color variation, a little desaturation of that brown, along with dirt and moss will definitely…
If you look at the concept, the cliffs seem to be made of tall jagged stones. right now your shapes are too uniform and evenly sized. I would recommend making 3-4 tall jagged stones and then simply crash them through each other to create the cliff faces. right now it would probably look too noisy with tons of small-medium…