We stayed at site 14, which is on the other side of the island and is only accessible on a boat. We kayaked from the park office and boat launch. The route was difficult for me, the tide was coming in plus a strong wind, it took us about an hour to get to the island. The site itself was perfect, much better than the rest as much as we could see as we looked around. It's located in the woods with a nice shady clearing, its own very private little beach. We kayaked to the beach and walked around to see the ferry dock.
Make sure you know the tide schedule. The water levels are changing pretty dramatically during the day.
We also experienced a lot of mosquitoes during the night on the island, but it probably depends on the weather.
The fires are not allowed on the island, which requires some thoughts around cooking and reheating food.
Overall I would say it was a very unique experience.