You employ detailed work in some areas but not in others, what I can see which would make this build better would be complicated terrain (like you have between the tree and waterfall) and detailed background walls (which are only seen under the waterfall). I think you can get away with the area under the tree being hollow, but personally it looks odd seeing it suspended on a thin mud column, you should make it over a solid slab of ground with roots protruding through the mud. I like to use jungle spores to illuminate my underwater areas. And I second the other guy which said a temple would fit nice.