I actually like a lot of the stone wall areas, they're interesting and could actually be really natural looking in a lot of areas, if not for the really hard edges you've got going on, and the bevel and emboss doesn't help much. The drop shadow too, I'd avoid that since coming from under the rock makes it look as if it's floating. Remember that natural shadows don't come from under a wall, they go on top of the wall and floor together.
The big rock in the center is really nice, but still has some nasty hard edges that make it stand out a lot. My tip? Blend those edges, and use some soft brushes on top of it to make it really look like the edges flow under the sand. Also I'd say darken up those little white glow-y areas along the edges. Toss a nice, long shadow coming off of it to show light direction and height (hand drawn, not a drop shadow) and it could look great.
The building walls are the weakest area, I think, I'm not feeling the texture there.The effort in a lot of places to cut around the texture to make it look more natural is a good idea, but the texture just does you no favors, and repeats too much. I never use a repeating pattern overlay if I can avoid it, I prefer to lay down textures manually so I can vary it up when I need to and fix issues. It's time consuming, but the result is much more controllable.
The floor tiles are also another thing I'm not crazy about. I don't know, they just strike me as too detailed, they draw the eye too much. If you're sold on using them, that's fine, but what I would suggest is you drop some easy tile pattern under them and then lower the opacity of the pattern you're using so you can still see it, but it's more faint and less jarring. Or just find something simpler altogether.
The ground texture though, I'm really digging. It's got lots of depth and I think it looks great. The little rocks around the building walls are nice too. Some shadows on those (directional, not just a black outer glow like the broken pottery) would sell them a lot more.