Nice start so far! I like the POV and how the viewer automatically follows the path. Well done!
If I may, I have about 4 suggestions for possible improvements:
I agree with Mohawk about the waterstream-idea. To add to his suggestion I think you should use a powerfractal with billow-noise function and stretched-along the axis the stream is following (either x- or z-axis).
Then add some slight negative displacement to get a carved effect.
Maybe you can also improve the scales of the models. The grasses are rather large and I think it would be great if you made them way denser, close to overgrowing the steep surfaces.
The fake stones is a good idea. Maybe you can add 2 extra layers with larger fake stones. Let's say the first extra layer is 3x bigger than current fake stone layer and then the next extra layer is 6x bigger than the current fake stone layer.
This will add nice variation. Also, don't forget to decrease density over scale. So, many tiny stones, not too many big stones. I'd suggest you increase the density of the small stones very much to make the surface look like grit.
Last suggestion is that there is quite much to see and already ~80% of the image is covered with terrain and models and thus it is already quite "busy". I suggest you either reduce the amount of clouds dramatically or even completely delete them. This way you bring more balance to the scene.
I hope you don't mind all these suggestion and find them helpful. If you need any advice how to do stuff then feel free to ask

Martin