We sailed on the Carnival Fantasy in March 2016 for our honeymoon. It was a 4 day Caribbean cruise with ports of call in Key West and Cozumel. Ocean view cabin was roomy and decent. It was spring break season so there were tons of spring breakers.
As for the ship, it felt quite small and outdated. The entertainment and activities were great! The comedy club is always our favorite. The service was spot on, from the room steward to our waiters. In Cozumel, we did the Atlantis submarine excursion and its a MUST do. We booked through carnival excursion and it cost $99 per person but was worth every penny. I am not a water person and this was such an amazing way (that didn't require swimming/diving) to see the ocean floor and wildlife. In Key West, we did the conch train tour which we also purchased from Carnival. It was a nice tour on a train open air vehicle. DO NOT sit in the front! There is no shade to protect you from the FL sun.