For reference: Carnival Platinum level cruiser. I've cruised exclusively Carnival since 1997. My age group 30-40.
What most have already said is true. I can confirm an environment that really caters to the party crowd on Carnival ships. The vibe on the ship is incredibly laid back, dress code is rarely enforced, and most people get away with doing things they really shouldn't. Depending on your expectations, or where on the ship you will be at any given time will greatly influence the vibe you'll get. One part of the ship may be filled with drunks, however there's likely an equal group of people chilling in a bar listening to live music.
IMO, the most influential moments will be the interactions you will have with other cruisers. I can say in my experience the cheapest priced cruises trend toward more negative interactions with other guests. i.e. Witnessing more fights, arguments, rude people in general. The best cruises I have had have been on the newest ships in more expensive parts of the year and these cruises have had incredibly positive experiences.
When it comes to raw facts, food is good, service is good, newer ships are very clean, older ships are clean (much better if they've recently underwent dry dock), older ships WILL show their age through damaged areas that haven't been refurbished. Most ships will feel very similar in the Carnival fleet, from the carpet to the decorations it's actually difficult to remember which ship has what because they are so copy/paste.
TLDR: If you set the proper expectation and give yourself the opportunity to be in the right place at the right time on the ship you'll have a good time.
Mark your calendar for May 12th. The hearing for the preliminary injunction in Florida's lawsuit is being held that day. The outcome of that hearing and potential ruling will likely make or break many of the policies being debated, and for many it will likely make or break their scheduled July cruises. It's a very real possibility a federal judge could rule in favor of Florida within hours or even days, to lift the CSO and allow ships to sail immediately. If that does happen the vaccine passport issue in Florida will be a moot point.