We took a Carnival cruise once about 4 years ago. I went with my Mom, son and daughter and it was their first cruise ever. It was only a year or so after that my husband booked our first
Disney cruise and we have never gone back. lol
It was out of Port Canveral (which we sail from all the time) and we were on the Sensation, which is an older ship and did not have the great areas of the newer or renovated ships Carnival has now.
My experiences with them were fine and acceptable for the price we paid.
Cabins:
We had to get two side by side, and I put my daughter in with my mother and kept my son with me. Both were Oceanview and contained two cots, a vanity and a toilet/shower/sink combo. It was a tight fit to get around in, but then again, that is what we paid for.
On Disney the cabins are bigger and we all manage perfectly in a Verandah stateroom. Not even the family size, just regular Verandah cabin. I love the separate bathroom plan.
Food:
The food on Carnival was good. Not knock your socks off good, but good.
No specialty restaraunts on the Sensation at the time. The MDR, was fine if chaotic and crazy. The service a bit slow and confused. Most times, they forgot to bring something that one of us ordered, and 3 nights out of 4, my Mom's food did not come out with ours. They forgot to put her order in, so I would wait and eat when hers arrived. The last night they managed to get all our meals out at the same time, which was a nice ending note.
The food on Disney is good and I like the variety of choice. We ate at Palo one night and though it was nice, it was not something I would do again and have not since that second cruise. The service is VERY good on Disney and we have never had things forgotten or even late in arriving compared to the rest of our dining party.
Entertainment:
The shows on Carnival are really not kid/family friendly. The one show we saw was more of a burlesque type of show with a lot of adult humor but it was tagged as a family friendly show. The positive is that it opened up some discussions with my kids and I about appropriate entertainment for their age group.
I did wander into the casino to try my hand at a few things, but didn't care for the smoke and décor.
Disney shows are family friendly. Even the shows they tag as adult only, are not as risqué as the one I saw on Carnival that was NOT adults only. lol
I did not see much in the way of too much drinking going on. It never seemed out of control and it was a 4 night cruise with stops in Nassau and Freeport.
I actually saw more drunk people on our January cruise on the Fantasy than on the 4 night Carnival cruise.
All in all, Carnival is not a horrible cruise line, but your expectations would need to be adjusted a bit. At the end of the day it is about spending family time and relaxation.