Where else can you cruise and have Mickey and Minnie and Goofy and Snow White and Pluto and Chip and Dale and Captain Hook and other favorite characters walking around and in the shows and dropping in the kids clubs?
Also, the timing of the kids programs. On
DCL the kids clubs are open from 9:00 AM until 1:00AM and if your child is there during dinner then they go eat with the club. I don't have personal experience on other lines but I believe several folks have posted that their kids activities close down during meals and you have to pay extra after 9:00 or 10:00 at night.
The other thing that really impressed me (other than it's been a fantastic place for my DD to work) was that the Adult Only areas are kept Adults Only so while your kids are in the club in a totally neat activity, you can relax by the ADULT pool.
Also, only Disney has
Castaway Cay. It's probably a little hurt right now after Hurricane Frances but they will get it fixed back up. Check out this thread
Why does everyone love Castaway Cay so much?
Last but not least, the family atmosphere. You won't have to worry at the shows if the entertainers will say something that you don't want to explain to your kids. It's clean, wholesome FUN without the raunchy humor.
Long story short - DCL is just different and special. And worth paying for.