This was my wife's and my first cruise (and last!) on Carnival. We had just gotten off RCCL's Vision of the Seas the day before, having crossed the Atlantic on RCCL after our cruise on Celebrity's Constellation around France, Spain and Portugal.
Here's my brief synopsis on Carnival:
Pricing: An attractive price lured us in to try Carnival
Check In: Pleasantly quick, considering we had no "status" on Carnival.
Cabin: Fairly standard size, amenities, and furnishings. Would have been fine, except it was WAY too warm for us. We contacted maintenance that first day, and when a technician arrived at our cabin, we were told that the 74.5 degree temp in our room was "within Carnival's pre-determined acceptable range of 72-74 degrees". In other words, Carnival tells you what temperature THEY think your room should be, and you are stuck with that!
Food: Surprisingly good -- better than RCCL. There were some quirks, however. The taco bar (the tastiest food option for off-hours dining) had limited hours, which [in]conveniently was always closed when coming off a Carnival shore excursion. The Pool Bar made popcorn, but on a "toy" popcorn machine which pumped out about a half-gallon every 15 minutes -- with a queue of 20-30 people waiting, it was apparent you would wait more than an hour for a small portion.
Crew: Good to very good. The waitstaff in the dining room (from hostess to assistant waiters) all were familiar with food allergies, and made ordering around the menu a reasonable exercise. Crew was generally courteous and efficient. It was our first cruise where we never saw the Captain walking around the ship.
Ports of Call: Here was the supreme disappointment. See below.
Shore Excursions: Pretty standard, but since all cruise lines subcontract out to local companies, no surprise there.
Fellow Passengers: The showstopper. In all our cruises, we'd never experienced loud partying in the corridors -- at all hours! Putting out a "Do Not Disturb" sign was as effective as the proverbial "Kick Me" sign on your back. People were rude in the dining rooms, rude in the hallways, rude in the bars (as well as being loud and very drunk), and people seemingly smoked everywhere.
In summary, the passengers made the cruise unpleasant. I guess we're just not Carnival people . . .