Hi Stuart,
This is magnificent. I love the fact that the clouds are rich, the water is well-rendered and has a silver surface. You did not go nuts by overdoing the saturation of the green vegetation which I see most often, the "hyper-velvia" look! I think you might look at the play of light on the hillsides and see what variations due to shadows of clouds you might be able top harness or at least to play with.
I would be most interested in seeing the stitch with all the irregular pieces and before a crop. You might find it very powerful to make a slightly larger rectangle and fill the extra space with black or else white. Anyway, it will be intriguing to see what it looks like, since we see in sections as we sweep around and meanwhile we might move our head up and down.
This is exceptional. There is no element that I would really want to see more of except the wood structure to the right. That's interesting.
In art, one should not be limited to straight lines. If odd shapes show the picture better, try it out, you might be very surprised.
The main thing is that this scene should not be imprisoned in a frame with ornate borders. It would, in my personal taste only, be great with a linen wide matt in an off white tope. The frame needs to be simple so as not to overwhelm this delicate scene.
Tell us how large you will print it!
When you tone mapped in Photomatix Pro, was that from 3 different outputs from a RAW program? Anyway, I like the discipline or luck that it ended up looking so natural. Often, HDR gets to look like some computer generated scene. Here, by your skill, or chance, you have retained the modest drawing of the trees and it's appealing!
Asher