Wow, lots of opinions here and many from divers who don't cruise or haven't done it for a long time.
We have started cruising the past few years, due to surgeries etc, which kept us from doing a dedicated dive dive dive trip.
Here is what WE have found, our actual experience, cruising with Carnival cruise lines, heading out on our 10th cruise in 4 yrs in April.
We have done 4 dive days (8 dives) all booked with the cruise ship. All good, no waiting for anyone to arrive, or issues. We took our own gear but most people only bring masks and fins. Its totally up to you. Every dive op we have seen through the cruise ship has had really nice newer gear and we always ask people how their gear worked, if they had problems. Zero reported issues on our trips.
Grand Cayman... tender port for all ships, there is no pier. You tender to shore, and meet your dive op at shore, they will have a big sign. Dive op is good, nothing overwhelming, but safe and clean and gets you out and back, that's all we cared about. We book thru the ship as our port arrival time was too late to schedule with a local dive op independently - this is something you have to check before you book the cruise if it matters to you. We don't care, diving is really diving, any dive is better than no dive. We did a wall and a shallow wreck. I have 2 videos to show.
Cozumel.... this is a tough one, and I know people won't like it but it is nearly impossible to book independently here unless you have a group of 4+ divers. The reason is the port arrival times don't work with the local boat schedules at all. Most ships arrive 8-9-10am, and boats have already gone out. So unless you have a group of 4 or more, nobody will hold a boat for you. We did diving thru the ship and it was so much less of a hassle. It was fine, did Santa Rosa and Tormentos. I have 2 videos to show. Since this trip, the dive op has changed used by all the ships. Reviews online people are raving about how good it was, better than the other group we had (Sanddollar). We haven't dived with them yet.
Half Moon Cay...private island, no diving, just beach day.
Ocho Rios..Jamaica, not known for diving.
We have also done cruise ship diving at Grand Turk and Roatan....both of those were primo diving. Dive op through ship and diving were top notched.
NO, we did not have cattle boat diving. Grand Cayman was the only one where we had a larger group on the boat but we were broken into 2 groups and had our own DMs. The other ports we had 10 divers or less, normal sized groups, with a range of skills for sure. Grand Turk was the best of the dive ops, we had 1 new certified diver with her experienced boyfriend as buddy, so he wrangled her both dives, and the DM spend rest of time with us. Fantastic dives. Roatan there was a group of 3 newly certified on the dives, and they were a handful for the DM, but since the diving was so easy, we just did our own thing and stayed with the group until time to go up. Easy stuff.
FYI - I had 500+ dives before starting cruising, Ron had 900+ and certified instructor and tech diver. We aren't noobs.
My
videos:
Grand Cayman
Cozumel
Grand Turk this past May
this is just a sample for you, as I said its good diving from a cruise ship, we will continue to do it regardless of what some of these critics say.