Enjoyable couple of hours on a catamaran and snorkeling. The reef with turtles is pretty far down and the water was fairly cloudy, so I didn't have a lot of success seeing turtles. My wife had close encounters with several. My poor vision and lack of prescription / magnifying facemask was probably a factor as well.
The guides were friendly and knowledgeable, and gave enough instruction that first time snorkelers seemed to be OK with the activity. Wear plenty of sunscreen or long sleeves, there's minimal shade available. And bring your own water - this isn't a party boat with drinks available.