We had an extremely bad cruise experience on the Carnival Sensation (6/4/09-6/7/09).
Strike #1: Following the advice of their booking agent, we accepted incorrect room assignments to save us money. The booking agent encouraged us to do this and assured us that we could change the room assignments at check-in. However, during check-in, the sign & sail room #s and credit card #s were improperly assigned and we were told that changes would not be possible! We elevated the issue to a "superior" and painfully got it resolved. The experience was unpleasant and embarrassing for our 13-year-old daughter who wanted to just go home at that point. She was the reason we took the cruise. She was being rewarded for getting good grades.
Strike #2: Carnival's website specifies that carry on baggage may not exceed 16"x24". The port authority made us check compliant bags because they "do it by eye". We were promised that our checked bags would be available by 1:30 pm. Subsequently, a time critical prescription medication was left in the bag that did not arrive UNTIL 4:30 PM, EXACERBATING MY WIFE'S HEART CONDITION.