Yup it was a nice cruise! Cozumel is the nicest stop for diving. It's a nice relaxing drift dive with lots to see. Also you can easily book a dive thru the ship or a private op as there are dozens available. I would go for a 2 tank myself, it's roughly half the day.
I dived in Roatan, Costa Maya and Cozumel on this cruise. No dives available in "Belize" (I put belize in quotes because the stop is not on the mainland but on a "private island" which is just a beach stop, so you're not really in Belize).
The dive in Roatan was with Anthony's Key again, fairly large boat but many DM's and divers split into groups of 4-5 by experience level. Plenty to see under water and quite a nice dive. During the surface time between dives we got to go back to the dive shop and visit their beautiful resort around the bay (I wouldn't mind spending a week there!)
The dive in Costa Maya was with Dream Time again and once more they delivered. We were a tiny group of 3 divers. The dives were quite nice and we enjoyed some nice canyons, but the water was a bit turbid with sand suspended. Lots of wildlife.
Cozumel was my favorite once again. We dived with with Sand Dollar on a huge boat. Fortunately we were split into groups of 4-5 according to experience and enjoyed a really nice long drift dive along the reef with a few swim thrus in mini caves and saw tons of wildlife. The dive boat picked us up right at the cruise ship pier.
Pat