Embarking on the Carnival Glory for a 5 nite cruise from Manhattan to Canada we were first time Carnival cruisers, with 4 other cruises under our belts. There is definitely a difference. Can't knock vacations, but Glory seemed to be densely packed. Yes, a cruise ship fills up with 3000 people and 1000 crew, but everywhere you turned you were cheek to cheek with people. The only place there was a little room was on the Serenity deck - adults 21+ only. Food was a solid "B" with nothing standing out. I stuck to fish for dinner and was rewarded. Others in our party ordered meat and were disappointed.
Fairly aggressive alcohol peddling - easy to say "no" - but when you say yes - those drinks add up quickly!
In summary, Carnival is welcoming for all sorts of folks, but don't expect quiet contemplation places - even in the library. "Fun" seems to mean packed with people.