I think you should darken the textures and make more distinction between grass and rock. I would also add some lateral displacements (PF, billows or perlin, stretched by Y perhaps: 50/200/10, displaced lateral or normal by 20m or so) after a compute terrain and add some strata broken up by a PF (billows, sizes 50/200/10 or so) after that. Work on the coastline too, darken soft area just above water level by color adjust on a surface shader.
And put camera where I put the arrow for a more dramatic view, perhaps.
Just some ideas....