I agree with Oshyan about trying to get everything done in TG2 if possible...
I think you did a great job on the postwork. Nice coloring, lighting and dramatic contrasts.
The concept is good and very well executed. To me this rock looks like the size of a schoolbus and thus seems a bit too big to be blown away by the wind on the mud...
Normally those stones are smaller. It doesn't really bother anyway.
The only thing that really should be improved in my opinion is to render the clouds again to get rid of te grain.
The rest of the image is so crisp and clear, a small pity the clouds aren't.
Nevertheless great work!
Martin