This is nice work so far, but I do have some suggestions:
You mentioned that rendering the reflective rocks takes very long. How did you add reflectivity? Using a reflective shader with raytraced reflections? If so, disable raytraced reflections. It renders ~4 times faster and there's almost no visible difference. You can also choose to use a default shader as base layer for your rocks and then set reflectivity using the specularity settings similar to that in the reflective shader. The default shader generates the specularity/reflectivity the same way as the reflective shader except that it doesn't generate it using raytraced reflections.
I see what you've been trying to do with the lines in the water
![Smiley :)](https://www.planetside.co.uk/forums/Smileys/fugue/smiley.png)
I like the approach but as said before the lines are too sharp and also to regular.
But I have to admit or make a remark about the water in Terragen.
In all previous version the waves of the water are 'always' 'horizontal'. If you want waves arriving at the shore you will always have to choose a pov from the beach rather then from the side like you did.
I think a function to rotate the orientation of the waves or to make them concentric would be very useful.
The rest of the water and the transparency looks very good, keep that untouched
![Smiley :)](https://www.planetside.co.uk/forums/Smileys/fugue/smiley.png)
I also like the variations in stones, though one fake stone layer looks a bit triangled.
The grass, trees and logs look nice and work well together. Looking at the stones I think you can even increase the tallness of the trees, maybe 1,5 times.
Those clouds are amazingly deep and thick. The distant hazy effect is nearly perfect to me
![Smiley :)](https://www.planetside.co.uk/forums/Smileys/fugue/smiley.png)
Maybe you can try to decrease fake internal scattering to give the clouds some more definition, beceause it's mainly blue and white.
If so you may also consider to increase the small scale size in your fractal. As you probably know the density roughness of the fractal roughly controls how well the smaller scales are defined.
Seeing the length of the post it seems a lot is wrong about this image, but that's nonsense. It's good work so far with a couple of very strong points and I think like your waterfall picture this has potential.
Martin