As you asked for critique, The rocks/wall looks pretty damn good. but if you want to add some realism add some more texture to the rocks ( grain and very small cracks ). Another thing is the houses in the back, it might look better if the houses where a little smaller. it makes the mountains apear verysmall yet the detail on the mountains suggest there big for some reason.
Anyhow the picture is great, and i love the coloring
I love it, you have a good contrast between light and shadows that makes everything look realistic. The rocks kind of look brickish but because you said wall, I'm assuming that was probably intentional. Good job!