The horizon line appear to droop downward, as if the lens has a severe amount of pincushion distortion. That kind of ruins the shot for me. I think the sky in the upper left-ish area is a bit too bright, and the rocks lower left too black. Re-processing the image, and striving for a bit more difference in tones in the middle values would help this I think. It probably looks much better seen large, on your monitor, than here on thee web at 640 pixels wide...