Thanks for the feedback 
I definitely plan on doing some adjustments to the rocks, will be redoing most of it and adding something to add a bit of variation to them texture wise will definitely help a lot too
I didn’t go with the new lighting model only because I suspect that its a lot more expensive with the subsurface scattering than the default lit mode would be. I think the lighting turned out perfectly as well on them, the issues I have currently lie more in the actual texture of the mesh and like you said the actual blending with the landscape, both color and the bottoms of them are very dark.
If by caustics you mean the water reflections on the environment around it no its not atm but would be a nice touch for sure