Wow, this is turning out quite nice. I do like where you are bringing the terrain, but I still think it is a bit too "real" for the overall style (at least in my mind). Of the terrain that you have done in the top left, I think the best result is the "dune" just above the tower just to the left of #9. The lighting, colors and textures all mix perfectly for what I see as the direction you are going in.
keep up the good work