The base is really nice. That really makes this project a complete project.
The entire scene is a bit clean. I would explore pastels and add a layer to the entire thing. A nice coating of a buff/light tan color. Something similar to the ground color. You could also look to add a bit of dark weathring to areas of the wall to make it look a bit older. Something along the bottom edge as if when it did rain the dirt and ground got kicked up on the wall. Maybe a few scuff marks on the opening in the wall. Just some suggestions.....