We did the Dolphin Swim in Ocho Rios and had a blast. It is fairly structured and you don't get unlimited time with the animals...but it seemed that we got alot more interaction than the "encounter" folks.
We were able to:
- stroke/pet (?) the dolphins
- dance with them (who were TONS better than the humans!)
- play superman (the dolphins pushed us up & across the water)
- fin pull
- watch them do various "tricks" like wave, jump thru a hoop, etc
I know this wasn't about Nassau, but hopefully it helps a little!