I extensively cruised with other companies including Celebrity, Carnival, Norwegian, and Viking River before I ever did my first Disney Cruise and like many of you, couldn't seem to figure out why anyone would pay essentially twice as much per person for what I at the time considered to be a kids cruise. After having a child, my wife and I decided to see what all the fuss was about, and outside of Viking River for their phenomenal Asian cruises, we haven't gone back to any other line.
Perhaps one of the biggest differences right off the bat is the sizes of the more basic rooms on a Disney cruise are similar in size to some of the upgraded suites on other lines. If you compare price per cheapest room across all lines, Disney is always going to be the most expensive, but if you compare the quality and size of the basic rooms across all the lines, Disney wins hands down. The last time I took a trip on NCL, I booked a mini-suite that was about $200 less per person than the basic Disney ocean view room for a similar itenerary, but the mini-suite wasn't as nice as the DCL ocean room and was almost identical in square footage. DCL isn't for cruising on the cheap, but their introductory rooms are the best in the business.
In terms of service, as everyone else has already beaten to death, Disney service is above and beyond. While other cruise lines do have some amazing staffers, it's usually the ones working for tips, where every crew interaction on a Disney cruise is phenomenal. It really is Disney service magic from the minute you are at the port to when they are getting you off. Whether you bump into a maintenance worker in the hall or are interacting with your waiter while dining, each interaction is so friendly and courteous. Every time we have enjoyed a Disney cruise we have made friends out of our table mates and our wait staff becomes like family by the end of the trip. I haven't really experienced that with other cruise lines outside of Viking River, but I find Viking River to be about as high end an experience as one can pay for outside of owning your own boat.
Entertainment on deck can't be beat on DCL either. For both kids and adults. My daughter lives in the oceaneer club while on the boat (its hard to pull her away), and if we want to do more adult excursions at port, it's a wonderful to have that available. The shows are great, and some of the adult cooking and drinking classes have been incredibly memorable. Any adults saying they're bored on a DCL cruise aren't trying or are to too intraverted to enjoy many of the group activities available. I think cruises by their very nature are social vacations, and if you want seclusion, you picked the wrong format.
The biggest seller for me is that while WDW and Disneyland are fun, DCL gives you the same kind of magical service and Disney experience without all the hassle, and for a very comparable cost. When I get back from a WDW vacation, I feel like I need to take a vacation from my vacation. When I get back from a DCL trip, I've travelled to places I've never seen, relaxed a lot, and am refreshed, all while feeling like I'm in the same Disney bubble that I love.
Overall, I find DCL to be worth the premium. That's not to say an amazing deal on another line won't pull me away, but from a financial standpoint, even though we can do cheaper, it's hard to do better.