You are so right about the Sensation being a great ship. We went on the Sensation in May and loved it. A month ago we got off the Freedom (which admittedly we liked more, but it's a bigger boat and more to do) but we are about to get on the Sensation again this weekend! Would we go back if we didn't like it? NOPE!
I think people just like to complain. The ones that do are usually spoiled and they are the ones who usually yell at the staff or try to make them miserable. Our only complaint about our cruise before with the Sensation is that we wanted it to be longer ;)