We loved it. My DS (who was 12 at the time) would say it was the highlight and favorite part of his cruise.
I had recommended it also to close friends, and it was a highlight for them as well. If you love snorkeling, this is a good excursion!
I guess what was the clincher for us, is that you beat the other excursions to the snorkel sites. The speedboat ride was very fun, and DS loved snorkeling with the turtle. (There was only one in the area, but we didn't care.) Most of the time, we were the only ones in the area...they would be just coming as we were already leaving. The boys doing it were so nice too.