Let me start by saying that this was my second cruise ever, so I only have one other ship to compare to: the Carnival Sunshine. All in all, I had a good time since I was on vacation, had a fairly decent time on the ship and enjoyed the three ports of call. Unlike other reviews, I didn't have any "Nightmares" or "Disasters". However, the ship has a long way to go.
So first, the good parts. The ship is huge, so there is plenty to explore. They have plenty of bars to get your drink on and food available at most times of the day. The ship is great if you have kids because there is plenty for them to do. The water slides (4) are fun, and they have a camp for toddlers. The shows at the theater were great, the comedians were funny, and the ship's band was terrific as they had various shows throughout the ship. The crew was always kind and helpful, and cruise director MarQ was lots of fun. Dinners were hit or miss, mostly just fine. Didn't try any of the restaurants that charged, so can't comment on those. Breakfast and lunch at the buffets were very good despite what others say. Then, of course, the destinations were wonderful.
Now the bad. There's one main thing you'll notice as the number one complaint from other reviewers: TOO MANY PEOPLE!!! This is the crux of the problem throughout the entire ship. With over 4k passengers, everywhere you go is crowded. The theater gets overcrowded, the lounges get overcrowded, the lido deck gets MASSIVELY overcrowded, and don't get me started on the pool situation. Carnival bills itself as the "FUN" ship, so obviously they're going to have a lot of families with children. Unfortunately, the kids take over the two small pools they have, leaving the adults to seek sanctuary at the Serenity Lounge (adults only) which gets full by 8 am. The lines for for the buffet are obviously long, but they move fast so there wasn't much issue there. Any show at the theater or in a lounge opens its doors half an hour before the start, and lines start forming half an hour before that. You spend a lot of time standing in lines.