Ok... Where to start?
This is my second, and my partner's first cruise. I had previously sailed with P&O out of Brisbane around 18 months ago, and while (for the most part) I enjoyed that cruise, I was not confident that my partner would enjoy this type of holiday. I can say though that comparing P&O with Carnival is like apples and oranges, each has its strengths and weaknesses. They are both budget options, but Carnival seems to attract a more vibrant crowd, is certainly more colourful, perhaps even gawdy. P&O attracted more walking frames and seemed less organised.
Anyway, about THIS experience...
I booked the cheapest possible fare, an inside cabin. When we received our room assignment, Carnival put us in a wheelchair accessible room with a window. The room was huge - the bathroom massive. The bed was too firm for my liking, but provided for a good nights sleep none-the-less. We asked for extra pillows which were provided with a smile. I don't think the thermostat was working, the setting made no difference at all to the temperature of the room, it was comfortable most of the time anyway. One silly thing that wasn't thought through... you need a credit card to use the in-room safe. There is no charge, the card just becomes your key, but I wanted my credit card in the safe, not carried around with me on the ship.