My family and I went on this excursion this past December and were really dissapointed. The stingrays were kept in a cage and were mutilated by removing their stingers and (according to the guide) their teeth. The area they were in was really boring for snorkling as well.
The worst thing by far was the infestation of sand fleas on the beach. Everyone that went on the excursion was covered in flea bites and the guides didn't have any bug spray at all. We spent the next 4 days doing nothing but itching and there weren't really any drugs on board to help with it.
Carnival reimbursed everyone that was on the excursion the 30% that was carnivals.