We just did the Boatswain's excursion to the turtle farm two weeks ago. I would recommend doing snorkeling at the beach to experience the beautiful waters of Cayman. We snorkeled at the turtle farm, and while my children enjoyed it, I did not feel like I truly experienced much of Cayman. Also the water in the snorkel area is very dirty. Lots of nasty stuff floating in the water (it did not seem properly cleaned or filtered; my one son got out because the water was so gross). There are several sea turtles freely swimming in the tank. You can attempt to interact with them, but they will most likely swim away. It is a very large pool, kind of like the shape of a long lazy river, and then a drop off area that is deeper. The beach area is some sand and beach chairs along the edge of the pool/lagoon.
I thought that the lunch buffet was adequate, about four or five items to pick from, with someone serving you from the buffet, and I did not feel like I should ask for seconds. Drinks are not included other than they have made some red koolaid and have tap water.
It was really awesome to hold the small sea turtles though. You can even step into the holding tank and stand there holding them.