Quite a nice render The water & terrain works quite well.
Photoshopped Render Bits:
Well, not bad, however, if you wanted the render to be more convincing (especially since this looks like a healthy terrestrial planetscape) You could implement tree's from stocks & such,
also your work with the waterfall is not bad, looks liek you smudged the waterfall? eitherway, overlay some textures like rocks underneath thewaterfall, also implementing rocks like its hanging out of the waterfall could add some nifty nifty depth
The planet in the sky is not bad, the blending of it into the sky is good,
it hides the often overused look of a greg-martin-tutorial type.
the colours a little funky, but not to bad, the ring is ok, but it dosnt have solid edges - if you observe a real ring, they have an edge, rings,
yours is like a swirling gas or something,
a planet ring has edges, this is why we should hate twirl filter!
Seem nice & calm, gives an attitude to the image which is nice.
Serene & comforting
Good job on that.
All in all:
A nice calm terrestrial space scape piece that is quite well done, but could do with a few more improvements