Before MSC Opera I was on MSC Fantasia which is a bigger (and better) ship. Overall impresion is great! Itineraries are great, time spent on shore excellent and everyone are so nice and kind. If this had been my first cruise I would probably be thrilled, but since this is my third cruise I couldn't help myself but to compare it with previous one. We were the first passengers since the ship was renovated last year, and one could say that this was a test cruise. There were a lot oversights: mugs and cups in buffet restaurant were often dirty - every second cup was clean so it became tiresome to check every cup. Juices in the self serving restaurant were available only in the morning not in the evening and hot chocolate wasn't available at all although it was included in the price. Later we found out that staff don't bring out bags of hot chocolate or they rarely do and sometimes they make a hot chocolate in the thermos which is not warm and which has very little cocoa (color was dirty white, not brown!).
Food for breakfast was the same every day; muesli was already prepared on the milk-it looked disgusting to me and I would prefer to prepare it by myself in yogurt. I drink a lot of tea (which was available all day) but I could find honey only in the morning and lemon is even harder to find. The food was often greasy (even fish!) and dinner in the restaurant was taking too long, every single day (from 9pm till 11pm!). Although maître d'hôtel came to us one evening asking us how is everything, are we satisfied and promised us faster service, nothing has actually changed.
The midnight buffet was very poor: mostly vegetarian sandwiches and dessert from previous days.
It is very ease to use public transportation to get to the heart of Athens.