My wife and I have only sailed on Princess in the pawst and this was our first time on Carnival. We had heard the rumours over the years, i.e. Carnival ships are floating parties filled with college students gone wild and drunken boors. Well as for that...yes we did encounter more drunks and people behaving badly compared to Princess cruising but not overly so.
1. Overall service was as good as Princess and in some cases (dining room) slightly better than Princess (this was a big surprise for us)
2. Shows were more entertaining
3. Cabin service, i.e room cleaning was excellent and food deliveries were good (except sometimes our breakfast orders were missing items)
4. Passengers tended to leave garbage and dirty dishes all over the ship and in the strangest places (next to the outdoor jogging track). Noticeable early in the morning despite the crew doing its best to cleanup overnight.
5. Areas that allow smoking have been reduced, particularly the cabins but is still allowed on the balconys. More than once we were forced back into our cabin due to neighbours smoking on their balconys. Its high time they banned smoking outright everywhere on all ships.
6. Like using the service kiosks to check up on ship charges instead of lining up at guest services
7. balcony cabins seemed slightly smaller and narrower compared to Princess ships
8. Excursions were fun, particularly the plantation/dolphin cover outing in Ochos Rios, Jamaica...although the plantation portion of the tour was so long that the Dolpin Cove part was cut short. No sooner had we had lunch and were in the water swimming it was time to go back to the ship..
Overall I wouldn't go out of my way to cruise on Carnival again but I wouldn't avoid Carnival.