A group of 15 of us ranging in age from 13-68 traveled on the Carnival Miracle Western Caribbean New Year's Eve cruise (Dec 31-Jan 7 '07). This cruise was tremendous fun and great value.
The ship's rooms, both the inside and outside cabins, are relatively spacious (closets and bathrooms too - plenty of room to turn around in the shower!) and are well equipped with exceptionally comfortable beds. We enjoyed excellent cabin steward service, a young and consistently friendly/helpful crew, a large variety of healthy and not so healthy food choices (their made to order oven pizza is not to be missed) and average to above average entertainment - the New Year's Eve band was great fun. The ship is kept immaculate by a large clean up crew and it sparkles. And there are plenty of ways to spend extra cash on this gigantic money making machine (casinos, excursions, bars, shops, etc.).
The first stop, Grand Cayman, is a wealthy, clean and picturesque island, with no visible signs of poverty. Some of us did off-shore diving near Eden Roc, a walk from the dock. Stingray City is a main attraction for tourists here. I was sorry we didn't see more of the island. The plentiful shops and restaurants surrounding the dock make for your typical tourist trap.
Cozumel was hit hard by the Oct '06 hurricane but is fully functional (minus the Carnival dock which made for another shore tender). Cozumel has beautiful reefs and water for scuba and snorkeling, small beaches, lots of places to walk around, shops near the center of town and a friendly, relaxed atmosphere. Mopeds can be dangerous, there are excessive accidents involving tourists. Please don't hire the horse drawn buggies, these sad animals are severely overworked, underfed and poorly cared for.
Belize City is dirty, ramshackle, full of pot holes and stray hungry dogs. It offers little for tourists. Poverty is evident here and it doesn't feel safe. Some in my group toured the city and came back depressed. I took a 45 minute water taxi to Caye Caulker on a recommendation from a Belizian in the tender crew and it was beautiful. Friendly, colorful, cheerful, sand streets with no cars (golf carts for taxis), lots of pastel colored houses and shops. There is a stingray tour from this island in case you miss it on Grand Cayman.
Costa Maya appears to be a Carnival trinket/excursion stop. You run a gauntlet similar to that on Cozumel but in Costa Maya there is little beyond the stores. We took a 10 minute taxi ride to the main beach/tourist area. The beaches were narrow with lots of sea debris. We were approached constantly by vendors. The locals don't appear to do well economically here, there are lots of hungry dogs, and behind the main street are some of the worst living conditions I have seen anywhere. Most in my group did a Carnival excursion, they said the beach was pretty.
Overall the on board experience was excellent - Carnival Miracle delivers the goods. This ship is as nice (though gaudy) and in some ways nicer than the Royal Caribbean line and it is certainly more fun. Excellent, friendly service, great lots to do for adults and younger, everyone in our group had a blast.
We would have preferred to spend more time in Grand Cayman or Cozumel instead of stopping in Costa Maya and Belize.