Have been on the Atlantica twice.both Eastern Carribean. We really enjoyed the ship. Very clean, nice cabins, good entertainment. Formal nights found most men in dark(although not all) suits..ladies mostly in nice dreses or pant suits. We saw a very few tux and gowns. VERY FEW. Mostly Americans onboard...varied age groups. It was a casual laid back ship with lots to do if you want to be active. Had a balcony cabin and loved it. Bottom line is...go for the fun and enjoy..dont worry too much about the dress..anything within reason works. We are going on the new Costa Mediterranea November 30, a sister ship to the Atlantica. Gonna try our first Western Carribean. The ship is identical in layout to the Atlantica.