Donna and Robo are right. These are four great islands and you shouldn't miss them. St. Thomas and Aruba have beautiful beaches, and St. John is a paradise just a short ferry ride away from St. Thomas.
Curacao has excellent snorkeling from shore and St. Lucia has lush scenery, rainforest, waterfalls, and a volcano. You can get around easily by taxi or rent a car if you don't want to invest in the ship's excursion. If you do a little research in advance, you can book many excursions on your own for less than the ship will charge.