Our family went on the Carnival Liberty for spring break, departing on 3/31. We had 2 families in total with 6 kids total - ages 2, 12, 12, 13, 14, 14.
We have been on many cruises - RCCL, Princess, Carnival, NCL, Disney, although we had not been on Carnival since approx. 1997. We chose this cruise because of the cost, and the itinerary. We were a little unsure what to expect after reading some of the reviews.
It was a fun cruise. It's a bit more casual and lively than the other brands I mentioned, but it was fine. The kids had a great time. In particular, the teens & tweens had a lot of fun, although not in a particularly structured way. They did not use the structured activities much. They mainly used the pool, sports court, EA sports bar, etc.
I would say that Carnival did a very good job with the comfort food ( burgers, tacos, pizza, etc ) in terms of availability & quality. The dinner dining room food & service was fine, but not quite at the level of some of the other cruise brands. But, it was not a serious detractor from our overall experience. It was fine.
In terms of entertainment, I would say it was analogous to the food. The informal entertainment was good - pool parties, music, etc. The formal entertainment ( evening shows ) were not really a highlight. I will say that the comedians in the smaller lounge were quite good, especially the adult shows ( at the family friendly shows, they looked a little tentative, at the adult shows, there were quite good ).
I would say there was a lot of variety in our fellow passengers ( moreso than on some of the other cruise brands ) - some were typical cruisers, some were spring break partiers, some were beyond description. That aspect really didn't impact our fun at all, but you should expect more variety than I've seen on some of the other brands.
Overall, the kids had a very good time. Parents had a good time. The ship was pretty clean. Stewards and wait staff were fine. Food was fine. Unstructured entertainment was fine.
If we found a good deal ( compared to RCCL or Princess ), and were going with tweens/teens we would go again.