The big
RCCL ships are nice... if you cruise other then disney, I'd reccommend only the newer, bigger ships. I did a 3 day on Carnival, it was like a trash can on the water compared to the Wonder. Soverign of the Seas wasn't much better.
I enjoyed my cruise on the larger voyager class with RCCL a lot, but I prefer Disney. I like
DCL because I love Disney, the shows, the characters, the service, the themed dining, the old ocean liner feel. I don't do a lot of the stuff bigger, non-disney liners have anyway. Only thing that might draw me to another line again is to see different ports. I have sailed Carnival, RCCL and NCL, but once I sailed DCL, I haven't sailed anything else since.
DCL is a pretty penny more... and RCCL's larger liners do offer a lot of neat things, like the rock climbing, ice rink, big exercise areas, etc... but like someone else said, it's not Disney.
Something about seeing Mickey when you get on the ship, running into Cinderella, hearing "When you Wish upon a Star." It's a magical feeling no other cruise line ever gave me, and I guess that's what I value more then the rock climbing, and ice rinks, and big casinos. Everyone wants something different out of a vacation, so best advice is to do research and think of what you are looking for in a cruise.
But if you love disney.. then you will absolutely love dcl, and will get hooked!