I have never sailed to the southern caribbean but am planning to next month. The western caribbean is kinda the same old stuff, and to be honest, the businesses in Cozumel are starting the get very pushy, more than they were in the past. They used to talk to you from the shops and say hi and invite you in. Now they are coming out to the sidewalk and trying to lure you in.
Costa Maya is a waste, not much to do at Merida...Grand Cayman is nice. It seems to me there are more interesting things to do and newer ports in the southern caribbean, but as mentioned, you can't exactly drive there.
And take cruise reviews with a grain of salt. Opinions are just that...someone's point of view. And there are some people who just hate everything. There was a guy on a cruise I went on who was on his cell phone as we left complaining about the french fries. WHO GOES ON A CRUISE TO EAT FRENCH FRIES?
Hope this helps.