Lovely capture of an extremely historic site, to say the least. I have the Nikon version of that lens and can well understand why you used it for this shot.
A lower ISO may have helped to capture richer tones, I have to agree with the commenters who see flatness in areas of the shot. The shutter speed is quite fast so you must have been shooting handheld. For architecture, landscapes, anything where your subject isn't likely to be going anywhere in a hurry, a tripod is worth its weight in gold. You then have a stable base and can close down the fstop, open the aperture and slow the ISO right down.
And, assuming that you did the pp in the order in which you list it, you may want to do all your cropping, image adjustment and colour manipualtion before you resize. Then usm and save for web. Wouldn't hurt to try!
I'm going through the entries, stopping at those images I feel have had the benefit of an unconventional eye and dwelling a little longer to try to see and appreciate what you saw. This is one of those images.
Positives: The bold processing has caused me to take pause and look more carefully at this image to to to discern what you were going for here. I can see that your curves manipulation do offer some drama - a bit like a lighting bolt effect in an old 'B' movie.
Critical stuff: Some of the tones here are just plain wrong to my eye and the very prominent foreground texture is quite distracting and it takes up too much of the frame.
Overall: The basic scene has potential but the final result falls short of the mark to my eye.