I have not sailed with Costa, but have been on MSC, with the European influence. Decor much subdued and elegant, a lot of pasta dishes, but that's not all that is served. Service was good. As an American, the announcements in 5 languages was new to me. The entertainment on my ship (Opera) was superb. Excursions were divided into groups according to what language you spoke. Mingling with others was limited, as each language speaking person segregated themselves in their own groups.
If price and itinerary was right, I'd sail Costa. I imagine all rules have severely tightened up, I wonder if even the ocean bottoms will now be explored for potential dangers thus charting new routes to travel.
I think rules on smoking are not as loose as they used to be. This surprised me, it used to be European ships were more lenient. Not so anymore!