I sailed on the Spirit Nov 14-22.
This was my first cruise with Carnival, and while over all I had a pleasant time, I don't think I'll cruise with Carnival again.
There was a strange smell I couldn't get away from. The exhaust from the kitchen (and all the fryers) and the dry cleaners and who knows what else was on the deck above my cabin (#8237) and the greasy/chemical smell was ever present on our balcony and it even got inside through the air conditioner. My traveling companion aptly called it "The smell of gluttony".
Then that smell mixed with cigarettes, which made it even worse. Smoking is allowed pretty much everywhere except the dining rooms, which is extremely unpleasant. People walked through the halls with cigarettes and smoked next to me by the pool and I had no recourse. I just had to take it. I couldn't even get away from it on my balcony. All of my neighbors smoked. Why can't smoking be restriced to areas where it won't cause non-smokers to suffer?
The food was overall very good at dinner, but all other meals were just mediocre. The chocolate melting cake, always on the dinner dessert menu, was wonderful. I think I had it four times.
Our dinner waiter, his assistant, and our cabin steward were all wonderful. The good service was a bright spot. It didn't make up for the smell, though.
There was also no enforcement at all of the dress code. I went to the effort to dress up and was hoping for a little imaginary grandeur on the formal nights, but there were people who came the dining room in track suits and tennis shoes.
Acapulco and Manzanillo were dumps, but Zihuatanejo was lovely. It was a charming little village with narrow brick streets and relatively well kept buildings.
I've cruised on Princess before and had a much more pleasant experience. Everything about Princess, including the passengers, is just a little bit more refined. On Princess I felt like I went to a resort. On Carnival I felt like I spent a week at a frat party.
I still enjoyed myself, but that took effort and determination and frequent visits to the steam room to get that awful smell out of my sinuses.