I've been on 6 Carnival, 2 NCL, 2 Royal Caribbean, 2 Holland America, 1 Celebrity and 1
DCL cruise. The only one I would NEVER go back on was Celebrity. The food was beyond awful, and inedible at times, and the ship felt like it shut down at 10:00 pm. The clientele was mostly senior citizens, at least on the one we were on. It could have been a fluke.
I honestly loved every Carnival cruise we went on. They were all 7 or 8-day cruises, and there has always been the same mix of people on them. About 1/3 families, 1/3 seniors, and 1/3 younger couples/singles. I have never seen the frat party atmosphere, but I have heard that it exists on the 3-4 day spring break cruises.
They have come a long way with their food. Some of the ships have burger bars on the pool deck which are run by Guy Fieri, who is a famous chef. They are excellent! The kids clubs are run really well, and when my kids were younger you couldn't keep them out of them. One of my kids' favorite memories was getting dressed up as pirates and going on a treasure hunt on Half Moon Cay which is their private island (not to mention one of the most seriously beautiful places on earth!)
It is interesting, but most of the people that I know who bash Carnival have never been on them--they all"heard it from someone".
i say go, enjoy yourself, and judge for yourself.
If you are interested, i've done a couple of really long, extensive picture reviews of the Liberty and the Freedom on Cruise Critic. Let me know if you would like the links. I've got lots of port pictures too. Which ones are you going to? We've done tons of different excursions, some good, some great and some awful. I would be happy to tell you which ones are which!
Have a great trip!