If you are going to drive through Monument Valley and go back, this is the place to turn around. Its worth getting to here to take pictures, not just of Mexican Hat, but also of valley of the gods.
Mexican Hat itself is a wonder of nature. How the rocks ended up like this is a miracle of erosion. It must have taken thousands of years for the rocks to get like this. You can get good pictures from the road, but there are also walks that get you much closer, so you can get some idea just how big the thing is.
Well worth a visit.