Great display of curves, and deep tones as Andreas said, but I think I notice a little CA up there as well. Really like that sweeping cloud just above the mountainous horizon though, is it pouring rain from it? Looks it.
Nice curves and deep tones. I like the foreground curve, but maybe a crop from the bottom to a 4x5 format might emphasize on the upper part a little. There also seems to be some kind of CA's on the edge of the clouds up there.