I shot this last week at London Bridge near Portsea. I really like the foreground rock and the sweep of the sandstone.
Canon 1DSMK3 w/ 16-35mm F2.8L - 2 Stop ND Grad - PP L.R 2.1
I think the greys look a bit dull; you miss what makes the image go POP. I'm also wondering if it wouldn't work better with a different crop. Try losing the right 25% and bottom 15% or so, taking advantage of the path made by the light-toned sand.
I'd advise against using the"clarity" slider with this one, there is already a slight hint of haloing around the large rock in the background.
Personally, I'd like to see this one in colour, or perhaps a discreet sepia.