Another difference I can tell you about Carnival and
DCL is that the cruise directors on Carnival are very visible and like to "pump up the crowd" so to speak with different events they have throughout the cruise. They are usually very outgoing and accessible. If you happen to sail with Matt Mitchum, you will surely remember your cruise as he is ALL over the ship getting people involved..and they are all also very humorous.
I think the best basic advice I can give to anyone wanting to try Carnival is to realize they are NOT Disney and do things very differently. They do inject a lot of "fun" into their cruises imo. Their service is great, their food is delicious and the ambiance is very outgoing. If you can go with an open mind and be open to a different type cruise I think you'll enjoy it. That's not to say you can't find a quiet spot to read a book and unwind, as you will find that too.
As I stated before, I'm all about variety, I like what each cruise line has to offer...right now my favorites are DCL, CCL and MSC....I'll venture out to other cruiselines eventually.