This was my first cruise, so I have only my experience and the reports of others to go off from.
The staff was friendly, though most assumed we spoke Spanish, and we needed to gently correct them often. Thankfully our waiter and room-keeper figured it out quickly, and spoke English to us when they interacted with us. They were kind, really all the staff seemed kind, even when struggling with English.
The food in the shared meal times was mediocre. Certainly edible most of the time, but nothing made me say "wow" or "Yum!" or "that was delicious!". There wasn't much variety day-to-day, and several dishes called by different names were actually the same as other dishes, especially the soups. Perhaps the exclusive additional-fee dinners were better, but we couldn't afford to buy them. We couldn't put our finger on why we didn't care for the food, but we think it might be that the food just didn't seem prepared fresh with fresh ingredients.
Yes, it's true, you can't bring alcohol or some foods on board. We were allowed to bring water and crackers and fruit, but the alcohol they "confiscate" and give back to you at the end of the trip. If you manage to get wine past the x-ray machines, as we met one guest who did, the staff won't have corkscrews to open it. Lunch leftovers were apparently forbidden, they made us leave the ship to throw it away. Yes, at every stop we had to pass ourselves and our baggage through one, often two x-ray machines every time we got on board, (this is where they confiscate the alcohol and record who it belongs to). Though at the end of our trip in Athens they didn't seem to care much, just waved everyone through.
The entertainment left much to be desired. Nothing sounded interesting or good, or in some other language. The one time we did see entertainment, it was very weak, but at least we stuck through it to say we saw one.
Not surprisingly most everything was expensive, or an added price. One surprise we didn't like was the mandatory 10 euro per person per night tip automatically added every day to our account. We didn't know that was coming, and that really soured our experience. We only found out by accident, and it turned our gratitude into bitterness. There's no heart in a mandatory fee, and since we weren't aware of it, it felt like a sucker punch. We're on our honeymoon on a tight budget, and they secretly add this expensive fee? That sucked. We found out a few days in by accident, but at the end of the trip during a disembarkation meeting in English, the Staff member told us that it had been added to our accounts (only when someone asked about gratuities of course), and based upon the looks of the other English speaking guests, they didn't know it was coming either. Bad form Costa. Maybe it's common, I don't know, but it wasn't a fun way to find out.
The bed was okay, not too hard or soft nor scratchy, but as a honeymooning couple, we didn't like the fact that the twin or queen-sized bed was made up of two single mattresses. Left an uncomfortable seam right down the middle of the bed. We needed to tell the front desk when we needed sheets changed, otherwise they don't change them.
Lest I be totally negative and neglect the good that was truly there, there were good things we liked. The ship and facilities were always clean and well kept. The staff was kind. The places we visited were good. The Daily update on places, weather, sea weather, excursions were helpful. The international breakfast option was nice to have. The lounge areas looked good for those who wanted to use it, and the pianist/cover artist was pretty good. The front desk staff thankfully spoke good enough English to help us when we had questions. They were accommodating of my wife's gluten-free needs, though the bread wasn't nearly as good of course.
