We put off cruising on Carnival for many years because of the bad press they had received. i.e "drunken, party ship", "poor food", "poor service".
We finally tried Carnival in 2000 because of a fabulous deal and have to say that we now regret not having tried Carnival before. We have sailed on five lines and Carnival holds is own with all of them. Each line is different and has its own advantages/disadvantages but we feel that Carnival is about the best value for your dollar out there.
If you are going for fun and are going with a positive attitude and you are not a chronic complainer I think you can have a great time on any cruise line.