We went on the Holiday in June and enjoyed the experience. The ship is the oldest and smallest in the fleet but has some of the best service in the Carnival fleet. Playa Del Carmen is a typical old Mexican town. Lots of small shops on a cobblestone drive. Few bargains but fun. Cozumel is paradise. Pristine water, great shopping and nice but expensive excursions.
You will regret having four adults in a room Two will be in separate bunks. The other two will be underneath one bunk. You will bang you head a couple times til you get used to it.
Keep in mind that the boat rocks and roars when changing directions and sailing into the gulf at high tide. We had a great time and we are sure that you will too.