I have no horse in this race as I've never done a cruise, however, I have been to Grand Cayman a number of times diving. We don't normally go to that side of the island but we did on one trip and I wasn't impressed. It's just a shopping strip that sells touristy stuff. We even saw a shop selling black coral, which is supposed to be illegal. You aren't missing much. I've also been diving in Cozumel and spent some time where the ships dock there (even saw the Disney ship at dock) and that area is a little better. While still a touristy area they did try to make it a little more local.