I won't go into a detailed explanation of why this cruise kind of sucked. I was a first-time cruiser, and everyone assured me that I would love it. Well...I didn't. The room was alright, if small. The bathroom smelled weird, and our toilet was perpetually stained and smelly. The ship felt like a cheap casino, only the decks had a timeless feel to them. The service was usually abrupt if not outright rude...since when is it acceptable to bark one word at a customer, and then bark louder when they don't understand the context in which you are barking the word "BEER" at them? Our steward was friendly but we rarely saw him, and he sure never offered his services to us.
The food was TERRIBLE. Bland, sloppy, and just gross. The buffet was confusing...they always seemed to be closing.
Key West was beautiful, no problems there. Cozumel seemed like one giant tourist trap, and most of the on-shore excursions were cancelled after we had disembarked (due to strong winds). We ended up spending a nice afternoon on a beach on the other side of the island, but I'm not really pleased with how it was handled. Also, walking around in the city was a nightmare, people shouting at us left and right.
The other cruisers were the WORST. I've never seen so much boorish, piggish behavior in my life. Pushing, shouting, shoving, grabbing at food, children running amok left and right...it just baffled me. The pool and hot tubs were perpetually filled with screaming children (or drunk adults, on the Serenity Deck). It looked like human soup. Someone pooped in one of the atrium elevators the first day on the ship.
I will not be cruising with Carnival again. In fact, I don't know that I will ever be cruising again.