We did that excursion on the 6/14 sailing. It was really nice. Prices were a bit high for food and drink ($10 mixed drinks, about that for a sandwich and fries). The beach itself was beautiful, although there was a barrier around the swimming area that made the view not so pretty. We didn't do the snorkeling, but those in our party that did had a great time. I just wanted more beach time than the hour or so you get after the snorkel trip.
We booked outside of Carnival (through Coral Breeze tours, the operator was Hammerhead Watersports), and had no problems with the service.