WE are doing this excursion next month, so I don't know first hand, but I will be glad to tell you what I have found out.
The boat is a lot of fun. (We did the same thing in Cancun, so I have been on the boat)
The boat ride takes about 30 minutes to get to the island, and your doing 360 turns in the water just about the whole time.
The island had been built up, until the hurricane came along, and tried to wipe it off the map. They have done wonders getting it back up to par, and it sounds like it is better than ever.
There are beach activities such as games, and water toys, and they have a little area of rides for the little kids.
The beach is suppose to be beautiful with hammocks and shade trees.
The food and drinks are included, and I'm told it is pretty good.
I do know of an independent tour group, but will need to PM you the info, so if you will PM me, I will pass on the info.
I have been to Coz many times, so if I can help with anything else you are interested in, let me know.