1) I notice that some of the grass is different. Subtle but thoughtful.
2) The placement of the structure and blocks is nice, it has a good natural look to it.
3) The diagonal surface, is that like the understructure to the building? It looks neat, I like how some parts seem worn away or possibly grown over. I might suggest some slight variance in the shading down the length of them to make it look dirty or aged or something. If it's something else then well idk depends what it is.