We did the full day a DePalm Island. We enjoyed it. It was less crowded in the morning than in the afternoon. Most people who picked the 1/2 day came in the afternoon. The buffet food was not that great, but the grilled area with hamburgers, fries and hotdogs were good. The snorkeling was really good. Lots of fish and the parrot fish were huge. The waterpark is strictly for kids. Staff asked us twice if we wanted to go early. Which was nice if we didn't like it we weren't actually stuck there. Probably wouldn't go back. It was a one time thing.
We did the Beach Express with De Palm, which I would recommend. We went to Baby Beach, Rodger's Beach and Mangel Halto. The best snorkeling we found was at Mangel Halto. Though you do have to swim out pretty far to get to the reef and the water was pretty choppy.