Hi ~
We did Blue Lagoon Beach day in Nov 2002. We found this an extremely, relaxing and very low-key beach. It's small, but also they don't book a large amount of people here so it doesn't feel crowded (at least it didn't when we were there). There is a limited number of hammocks so scout one out as soon as you get there. The water is very calm (no waves) and not very deep in the lagoon. I recall tube rentals there but can't remember much else about water sports ? We brought our own snorkels and masks and got to see a small shark, sea urchins (wear water socks !), a barracuda and other smaller fish. The one side of the island where the shore is rocky and there are waves is off limits to swimming.
We found lunch to be "ok". I recall chicken and cheesburgers and both were ok. I remember each person getting a ticket for a free drink also and we chose fruit punch. We packed bottled water and brought it with us on this excursion. They also have a volleyball net off to the side of the beach and we ended up playing with some other guests at the end of the day.
All in all, the beach was small with lots of palm trees around and hammocks hanging from them. The water was warm (early Nov), clear and very calm.
I will add, the walk from the ship to the dock where you board the boat over to the island was a stiff hike. We were fine, but my 67 year old mil had problems. She wasn't in the greatest of health as she was undergoing chemo and radiation at the time, and she had to sit and rest several times. We actually got separated from our tour group because of her slower paced walking and my dh and ds had to run up ahead and ask them to wait for us. I was sorry we didn't bring a wheelchair but we had no idea of the walk. I'm just mentioning this in case you're traveling with anyone who might have problems with a fairly quick pace walk through the town to the dock.