I have not found anything in the Captains Circle program that makes it outshine any of the other cruise line programs. Like other programs you get invited to past passenger get togethers onboard the ship. Like other programs you may get notification of some exceptional last minute prices. I do like the free internet after 6 cruises so I can check on my business email.
There are a few nice perks but I wouldn't say they are any better or any worse than any other cruise line.