We've sailed on Royal Caribbean as well. In some ways it was obvious that Carnival is the cheaper option, buffets aren't always available, the entertainment was a little hokey, and the cruise director seemed most interested in getting us to buy things. However, the food was much better than Royal and our cabin was bigger even though we had a balcony on Royal (interior this time). I liked hearing the water at night, and waking in the dark was a little disorienting at first, but since we spent most of our time on deck it was worth it to save the money. For the most part the drinks weren't any more expensive than most restaurants, and you can bring one bottle of wine per person which also keeps that cost down.
This cabin is handicapped accessible, which I had not realized at the time. That may be why it was so much larger than I expected, including the bathroom. This cabin is underneath the bridge and above the children's space, but we had no problems with noise. Lots of closet space, but I would bring hangers and those boxes that fold flat for using on the shelves. The drawers they did have were very small.
Having no window made waking in the dark a little disconcerting, but worth it to save the money and spend it elsewhere. Being at the front of the ship we always had to walk to the other end for food, but with so much of it available the extra exercise was probable worth it!
The Serenity, adult only, space was also much nicer than what we had on Royal Caribbean. That one was inside with windows. This was on a deck at the back of the ship so lots of sun with shade for those who wanted it.
I liked Carnival quite a bit, pizza was always available when the buffets were closed and the ship itself was comfortable and easy to get around on. Staff were very helpful and they organized the tender exits well. I'd sail them again.