I might have tried this at a different time or day, as the grey sky blends in a lot with the coloring on the building, causing it to look as though there isn't a lot of contrast. The focus is excellent, but I would have rotated the shot about 1 degrees counter-clockwise.
This is a potentially beautiful shot, however the angle is tilted which is offputting, the sky is grey and miserable, which in itself is not bad but with the extra spiked turret to the right, just seems like a dreary snapshot of a holiday to italy.
If you even cropped out the extra turret and rotated the tower so it was straight, tweaked the levels a bit more - this would actually make an awesome picture in my opinion, but then again, what would I know ;)
This is a beautiful photograph. My only advice is that it needs to be lightened a bit so that you can clearly see all of the details. It also needs to be rotated about 1 degree counterclock wise.