If you are coming in by cruise ship early in the morning or leaving in the evening, there are absolutely spectacular views to be had of El Moro and the harbor in general. At noon, especially if it is cloudy, it isn't so photogenic.
I wanted to visit El Moro when we came here in the fall of 2005, but it was too far away from everything to be feasible. It is a long walk in to the lighthouse from the street. (There is a lighthouse there in addition to the fort.) Instead we visited Ft. San Cristóbal which is also a National Park Service site.
According to Guardia Nacional de Puerto Rico - Historia y Tradiciones
by Jose Angel Norat, 1987. In 1584, the construction of the Moro Castle, on the east entrance to Puerto Rico Bay, next to the town of San Juan was begun. This fortress was completed by 1608 and was heavily fortified and armed with large cannons. Typical of most important Spanish cities, walls were constructed around the city, with large gates that were sealed at sunset. Shortly after the completion of El Moro, the fortress of San Cristóbal were begun close to El Moro, as well as smaller fortresses around the bay, for it's defense. There is a story that while El Moro was being constructed, the King Philip was found staring into the western horizon one afternoon from his palace, El Escorial. Someone who had been observing the King for a while, approached him and asked him what he was trying to see, so intensely. The King answered, "I am trying to see the walls of El Moro in Puerto Rico. We have spent so much money on the construction of that fortification, that I calculate that we should be able to see it from Madrid."