This was our first Carnival cruise, but we had sailed on Royal Caribbean previously. First let me say that the ship is gorgeous (less than 2 years old) and feels very spacious - even our interior cabin was larger and nicer than similar cabins on RCCL. However, the staff aren't up to par with the nice accommodations. Rarely did we get a "hello" or smile when encountering or passing staff. By the 6th day of the cruise, many were downright rude and it was obvious they were ready to be rid of us!!
This cruise has three "at sea" days and three port days. The first at sea day was okay, I was interested in laying by the pool, exploring the ship, spending time in the spa and with friends. By the second and third at sea days, I was getting a little bored. Carnival definitely needs more planned activities when half your time is spent at sea. I cannot speak much regarding ship-sponsored shore excursions, as we opted to book independently. I can say that going independently we paid 1/2 to 2/3 of the ship price for similar excursions. Most of the group that we travelled with (first-time cruisers) booked ship-sponsored excursions and were very pleased with all of them.
Meals were pretty good, but not exceptional - not as good as on RCCL. The nighttime buffets were a joke. Yes, there was 24 hour pizza - I had read raves about it, but it did not live up to them. There were plenty of waiters making the rounds of the pool area to take drink orders. I had heard of Carnival's "party boat" reputation. I saw a mix of ages on this cruise, and did not encounter any more hard partying than on previous cruises.
Overall, if this were someone's first cruise, I think they would come away very pleased with the experience. But if you've cruised with anyone else, you will realize what you're missing.