Whoa, the middle part, with the jungle suddenly changing to black looks really pretty awful. You ought to put a fade.png in there to make it blender better. Same for each side. Also, I would mess with the opacity on the clouds to make em' less harsh, and I would change the background color if I were you.
The middle ravine just looks kind of awkward because the tree background... if it were a ravine, there would be hillside in the background, not layers of trees unless the whole map is set on a hill (that you just have to assume exists).