I've just got back from the Costa Atlantica. It was my first "real" cruise so am unable to compare with other ships. However I was really impressed. The minus points I'd seen mentioned in various places (too many Italians, too much smoke, lots of announcements in 5 languages) were either untrue (the smoking) or didn't detract from the experience. There were a lot of Italians (2000 versus 47 English speakers) but as long as you hold your ground in the queue for the restaurant, this isn't a problem.
The English speaking host (Jason) was excellent - although one tip, don't mention what your job is if you do anything financial or are a teacher, as he'll have you up doing role plays. If you go on the ship this season, say hello from Fiona and Ian (the Inland Revenue economist) from London.
The music on board was mostly good, although there was one duo that tested my ears somewhat, and the drummer in the "Big Sound" band seemed to be mostly miming to the backing track.
We had an extremely good deal with Airtours which included a week in Lake Garda, however it meant we had an inside cabin on deck one. Our cabin was 1177 and was excellent (better than our hotel room in Garda). However there seemed to be a lot of vibration further aft (about two-thirds) back. I would definately go for a balcony next time. More than anything, seeing this ship docking is amazing - I've seen much smaller boats which are not as manouverable as this one.
Our tour guides were excellent - we did a tour in all the ports except for Bari - and would certainly recommend doing the extended tour in Istanbul.
The only disappointment was the pools on board. They seemed to be more artistic than functional, and once some lively children got in them there wasn't much room for anyone else.
That's all I can think of at the moment.