My 2 crits:
Grass:
It's not too convincing as grass to me, that may be because you wouldn't often find a waterfall like that, with the grass coming up to the edge of the water as well as the edge of the cliff.
*shrug*
Water:
Not too much I can say about the water, it looks nice, but it could use a little splash to it.
Edit: use alot more white or lighter blue where the water is actually falling, that should greatly improve the look of it.