I was on only one Costa Atlantica cruise, but overall the entertainment was superb. I wonder if it's the Italian tradition with the opera? They had a really memorable "revue" which was a history of Italy; they also had a very fine operatic tenor. They had a couple of shows (comedienne, magic show) that were ho-hum but over the course of the week I was quite impressed.
I also really liked a classical duo (pianist and violinist) who played in one of the lounges before dinner. Not that many people came with any regularity, but I was there every day and they did some smashing things: really classical music, not "lite". There were some lounge singers too who we felt compelled to visit every night. The entertainment was much better than I would have anticipated but it might have just been the particular match: me, the opera lover, with an Italian ship, paying tribute to classical Italian opera. It seemed that the more Italian they kept it, the better it was and the one attempt to do something a bit like Vegas palled in comparison.