Hm,first:change the rocks,they don't look realistic in that way;second:the positioning of the plants can be improved, vary their sizes,put in more plants and add some ground,this kind of plants do not grow directly on solid rocks.Third work on the water surface,add more ripples where necessary and some fog above the waterfall.Last point:change the position of the camera,it is too "central".The whole scene looks too symetric to me;asymetry should enforce the dynamic of the composition.One tipp to the end :keep on working !:-)

http://www.fredivoss.de 

...yippi ah yeah or something like that...