My first impressions were that the ship is huge. It's 260 metres long so some parts of the ship involve a long walk. The ship is decorated to Italian tastes - a little garish for English reserve. Until you get used to it, it can be difficult to get your bearings. This isn't helped by the fact that one of the formal restaurants takes up the middle of two decks so the route from one end of the ship to the other often involves changing deck. Costa has a number of ships built to the same design so I suppose regular customers get used to it.
We had a balcony cabin on Boheme deck. It was a reasonable size with plenty of storage space. It would not be particularly comfortable for people who like to sit in their cabin all day, but it was perfectly adequate for sleeping, washing and dressing. The TV was up near the ceiling in continental fashion. It had BBC News and Eurosport so we were able to watch Andy Murray get kicked out of the French Open in German.
The food was excellent. I have read criticisms of Costa food, but I presume this is from people who are unfamiliar with Italian eating. We had breakfast and lunch in the buffet where there was plenty of everything. By moving from the buffet out to the pool areas and back, you could eat and have coffee non-stop from 6:30am to past midnight. We had dinner in the My Way restaurant where the service was good. The Italian style is to have lots of small courses rather than a large plateful. With antipasto, soup, pasta, main course, salad, cheese and desert, you didn't go hungry (and you could always top up in the buffet if you did!). Since our trip included a wedding anniversary, we could have paid extra to eat in the club restaurant, but we were quite happy with My Way.
There was plenty of music onboard ship - not all of it to our taste but probably something for everyone. The speakers on our deck playing the love duet from La Boheme over and over again got a bit wearing after the first week. Entertainment in the theatre was interesting rather than spectacular, but helped to relax us before dinner.
The only real problem we encountered was caused by the sheer number of people - only to be expected on such a large ship. When over a thousand people needed to get from the theatre at the bow to the restaurant at the stern, and midships were blocked by the other restaurant, it was a bit like rush hour on the London Underground. At the last port of call, we had to go ashore by tender and we spent more time queuing for tenders to go and return than we did in town. Costa really need to address crowd control.
Overall, the cruise experience was excellent and I'd certainly sail with Costa again - although I might choose a smaller ship.