I was with a family group of 25 on this cruise, so interacting with and meeting others was not a priority. If I had been alone, however, the predominantly foreign crowd and lack of English announcements and activities would not have been conducive to socializing.
The stateroom was very nice, and I liked the layout of the ship. I'm not big on activities, and with early and late happy hours, when not on excursions or eating, a lot of my time was spent in the bar. The happy hour is 2 for price of 1, but they must be identical drinks. OK, so I'll drink some more. Wine and soda/water packages kept the price down at meals.
The dining room was very nice, with elaborate multicourse meals. The ingredients are put on board at the beginning of a cruise, and I would have preferred simple, fresh foods. The pizza at the bar is good late at night, and I never went to the midnight buffet (except on a tour).
I went on all the official Costa sponsored land excursions, as I figured they are guaranteed to get back to the boat on time. Every tour was excellent, with good busses and guides.
My main gripe was the poor air conditioning. When the dining room doors open and hundreds of bodies pour in, the temperature rises 20 degrees and the AC can't keep up. The mediterranean is hot and humid in the summer, and it was uncomfortable most of the time on board. The heavy cigarette smoke doesn't help either.
For a follow-up cruise I would be inclined to look toward a cruise line that is geared to Americans, as I believe the AC would be up to snuff and smoking would be curtailed.