On our recent Royal Caribbean cruise I ran into a rather boorish person who bashed Carnival solely because he cruised with them 20 years ago and it was a 4 night party boat full of drunk college kids. That was then, and it was often true - back then. Carnival changed their focus in a big way in the late 1990s. They really had a culture change and went after mom and dad and their 2.5 kids, along with grandma and grandpa too. It wasn't so much out of sense of altruism as it was a motive to increase profits. Families spend more money than college kids and they don't break the furniture or vomit on the decks.
Carnival led the way in raising the drinking age to 21, refusing to book anyone under 21 unless they had someone 25 or older cruising with them, and other policy changes.
I love cruises with Carnival. I think they give more value per cruise dollar than any other mainstream line.