We went on the Carnival Glory in January. One of the best excursions we took was in Costa Maya. It starts with a bus ride from the port. Takes about 1/2 hour to get to the private beach where we boarded a 2 person boat and followed a guide out to a platform out by the reef. The guide took us around the reef pointing out things like starfish and different types of coral. The water was fairly shallow and crystal clear. The reef protected us from most of the force of the waves. We were able to stop periodically and stand on the sandy bottom to rest. We saw many species of fish. The best part was seeing 6 squid swimming in formation.
With the open bar, good food, great service, and amenities (clean restrooms, gift shop, lounging chairs, waverunners, kayaks, and friendly people all part of the initial proce) this was the best excursion my wife and I took on this cruise. I recommend it for anyone looking for a great time.