A couple of ideas to make the scene even better, use a smaller particle size for the waterfall and set blur power a bit higher(bluring only in version 4). Turn the splashes on, so you get a bit of spray on the sides. put some rocks at the bottom of the waterfall, this will create some very nice random variations and disturbance to the water. Use a smaller tiling patern for the rock texture. I would take away the sharp point at the right side of the waterfall and make it more natural looking. Set a higher resolution to the landscape mesh. These comments are not meant to say the picture is no good, do not take it wrongly. There is great potential in the picture, with a little work, there is more detail to the landscape in mesh resolution and in the waterfall. I do not know which version you have used to create this, so i have tried to give some general pointers. I like the perspective and sense of depth in the scene. The ferns do not match, i woulr replace them with some higher grasses in a little bit different color to waht you have now for grass. Overall it really has great potential.

I think, this is a very diffulicult task for WB, but waterfalls are nice objects. The terrain is excellent for this exercise, so keep on making like this! I would give the same tips as Dimitri, the secret is:patience ;-)