Have a great time and don't tempt the sharks too much. Loved snorkeling in the Caribbean but was in Freeport close to 15-20 yrs ago and it was a seedy place then. Was there three days and the beach and snorkeling were great and conch salads weren't bad but, too many drug issues and unemployment with everyone trying to part you from your money.
Snorkeling time in the water was too brief for what you were paying. On a cruise ship you won't have that issue.
I hope you have fun and get some great food and great times