Disney:
Food - Good to Great. Some of the buffets are tailored towards kid food (chicken nuggets, hot dogs, etc) so you miss a little variety for Adults.
Managemnt of kids- Great (probably best in class) they offer activities all day that y our kids can join any time, they notify you if your kid needs you and they can find your kid anytime
Entertainment - Great (IMO) the stage shows every night were a must see for us; G - PG13 rated but good stuff
Service - Great
If you like Disney "Stuff" (even a little) and/or if you have kids under 16, I highly recommend it. If you like to hang out in bars, gamble, or watch/participate in adult games (hairy chest contest) it is probably not for you.
Also, make sure you check out all the costs of your trip. We did Disney two years ago and Carnival this year. To get on the boat, Carnival was cheaper, however we found the excursions through Disney to be quite a bit cheaper. Overall, the extra expense for Disney wasn't as much as it appeared, and definately worth it.
As far as length, we were on a 7 day and it was great. I have a friend that took a 3 day and wanted to stay longer.