For me it is first the itineraries, as the classic ships have variety and length, are not stuck into either the 3/4-night Bahamas milk runs, or alternating 7-night Caribbeans. Next is the size, while the classic ship smallness would seem to be a detriment, it is actually a huge benefit as you have much fewer people. This means at onboard events, you are have fewer people attending them, as the number of events scheduled are not based on the number of guests on the ship, but rather the length of the itinerary and the number of sea days. Even though the newer ships are bigger, they did not make onboard amenities, such as pools, bars, etc, larger in the same proportions that they added guests between the classic ships and the newer ones. Yes, some of the big items are missing, AquaDunk, Satellite Falls, MDA, etc, but those things have much more people trying to use them in a limited amount of time. Honestly, on the classic ships, I have never felt anywhere as crowded as on Disney Fantasy, or especially Disney Dream, which has far more first-time cruises adding to the crowdedness as they wander around lost, often just stopping in major thoroughfares and coming off elevators trying to figure out where they are going.