I am also curious where this will end up.
I don't buy the big rock with the rounded, curved sides, though, and I think there should also be vegetation on the steeper slopes. Overall I think you still have to find the right "mood" for the scene. However the scenery gives you a lot to play with.
You could also try Martin's Rock Surface on the walls, with different colors, though, not the stock red rock.
There could also be plants in the water.
Cheers,
Frank