Castaway Cay is great. Did 2 Disney cruises and booked another for next year. I went to the family beach which was near the bar-b-que. They have parasailing, jet skis, rafts, and a beautiful beach. There is a beach for the kids; a separate beach area for teens; a family beach; and an adults only beach. They had music and of course some of the Disney characters besides Mickey and Minnie. There were plenty of chairs available. The food was great and plentiful and free soda was also available. I'm sure you will love Castaway Cay.
My husband and I did a Disney cruise summer of 2003 and I have to say Castaway Cay was definitely our favorite part (and we LOVED the cruise so that's a big thing!). We did the adult's only beach on the island and it was amazing. So secluded, waitresses that cater to you, massage cabanas right on the beach, etc. They have a bbq right there...so you don't have to leave the island for anything. We just went by the other beaches, but they all looked great. It's a huge perk! We're going on RCCL this December and we're really going to miss Castaway Cay!! Have a great time if you decide to do Disney!