Just my humble opinion, but I think the straight-edges of the buildings take away from the overall look. You have these beautiful hand-drawn cliffs and hand-colored water, and then the buildings kinda look pasted on with a computer. I think the scene would look even better than it already does if you went over the buildings' lines by hand and took out the razor-straight lines.

Other than that, you could also add farm fields, a couple trees here and there, etc.

PS -- just scrolled up and saw that Gluhoded had basically already mentioned that part about the buildings. So, I suppose I second his statement