We are Americans who sailed on an August Mediterranean cruise which stopped in Palma de Mallorca, Cagliari (Island of Sardinia), Civitavecchia (Rome), Savona and Marseille.
The culture.....I had read numerous negative reviews about this cruise line by American passengers. I can only surmise that they have had minimal exposure to other cultures. Frankly, the offering of this cruise line is like any North American ship on which I've cruised. Unless you splurge on a high end line (i.e. Regent, Crystal, etc.), I'm sorry folks, every cruise is the same-- lots of human bodies, plentiful food, garish decor, entertainment galore, loud music, sun worshipping, waiting for elevators, the list goes on! Quite literally the only difference on Costa is that Europeans are the absolute majority-- with a healthy smattering of Asians, a small handful of people of color, and virtually a minuscule number of Americans. However my observation is that cruise passengers are exactly the same no matter the language they speak or the country from which they hale-- they simply enjoy this type of vacation. The only tangible differences that I noticed which may make some American travelers uncomfortable are increased smoking habits, a much later (and much louder) nightlife, and some Europeans who are not warm-fuzzy, dying-to-greet you types (although are universally receptive to your overtures). What's the cliché saying, "when in Rome...." I'd suggest embracing the variations in people and culture or stick with a North American cruise.
The cabins.....We had a triple balcony room. Plenty of space with 2 beds together to make a king and an additional twin. Sizable balcony with 2 chairs and table. Exceedingly generous closet space, but a bit short on drawers. Safe for valuables. Nice and varied lighting options. Two outlets, but only one that will accommodate your American electronics, so bring an adapter. Linens not luxurious but decent and plenty of towels replenished multiple times daily. Bathroom had generous shelving for toiletry storage and a drying line, but no outlet. Pool towel replacement, however, was quite spotty. Housekeeping, and I am super picky in this regard, kept the room spotless and did so at least twice daily.
There are cruise-provided shuttle buses (for a fee) and taxis available immediately upon disembarking. Private tour companies can also pick up right there. FYI the airport is about 30 minutes by taxi and costs 39 euros flat fee. It is possible to walk out of the port but the area is rather industrial and without services.
Easy exit from ship directly into town with a plethora of amenities. Cathedral and Caves of Drach enjoyable.
The port was actually CAGLIARI (on Sardinia). You disembark and wait a number of minutes (5-15) for a shuttle bus to take you less then a mile out of the port, where you can meet private tour companies and access town. FYI when I visited in August, there were many company representatives waiting for disembarking passengers with which you can book on the spot tours in the event you haven't done prior planning. Su Nuraxi and visit to wild horses of enjoyable.
You disembark and wait a number of minutes (5-15) for a shuttle bus to take you less then a mile out of the port, where you can meet private tour companies, find rental cars and access town. FYI when I visited in August, there were many company representatives waiting for disembarking passengers with which you can book on the spot tours in the event you haven't done prior planning. Option to avoid going into Rome is a road trip toward Tarquinia (Etruscan museum and necropolis) and Viterbo, where you can dip into thermal baths at Terme dei Papi.
There are both cruise-provided shuttle buses (for a fee) and taxis available immediately upon disembarking that can transport you into the center of Marseille. It is possible to walk out of the port but the area is rather industrial and without services. Also a few souvenir stalls right at disembarkation point. Exploration of Provence possible from Marseille, with Arles and St. Remy being lovely choices.
Easy exit from ship directly into an area of town without many services. Taxis available. 10 minute drive to train station. Exploration of Genoa is possible from Savona, where there is the world's second largest aquarium.