Half Moon Cay (a private island owned by carnival)was average. There wasn't much to do aside from going to the beach. On the beach my family and I had a blast when we entered the Sand Castle competition...sadly, the sea washed it away. The boat could not come too close to the island, so ferrying back and forth was a bit of a hassle.
This port was my least favorite of ALL cruises I have ever been on. It was just a bunch of shops from Carnival. After getting off, we got right back on. I suggest doing the same, its a blast in the pool area alone! My sister, however, did take an excursion--well let me rephrase. She and her daughter (7) were offered from a taxi driver a $20 charge to be taken to the most "beautiful" beach in St.Thomas. Apparently, this was not the case. 1ST, the $20 only counted for one way. 2ND,the cab driver left them at the beach, and 3RD, the beach was HORRIBLE and strewn with trash! Definitely glad I did not go!