Very nice! I love the feel of this.

The bump on the bottom section of the wall is excellent; you might want to tone it down a bit on the top, though. It looks right now like someone chiseled deep holes in an otherwise smooth surface. Some more noise in the bump would also help here.

If you're going for photorealism, the blue sky looks a bit wrong considering the yellow look, like Pony said, but if this isn't exactly supposed to be realistic than it makes a very nice contrast with the yellow of the rest.