Costa Cruises is really awfull. I have never experienced such a bad taste, bad service, bad food, bad acomodations and very bad common areas. I have done a lot of cruises including the "high end" like Silversea but also the "standard" ones like Royal Caribbean, Celebrity, etc., which by the way they are also going down all the way in terms of quality and service; and ironically Costa costs as much as the other "standard" lines; but Costa could be compare with a one stra hotel or less. They are in this business just for the money.
When you take a cruise you know you will be at their will for the time of your trip but Costa has cross the line between being at their will and trying to squeeze you with the most esential needs, not of a traveller but as a human being. The line doesn't even let you have drinking water for free in your room or in the restaurants, you have to pay for it; the bathroom in your cabin is more than essential. No shampoo, no conditioner, no body lotion (bring yours as lots of bottled water) and the cabin is so untasteful with also the more essential amenities that you feel like in a YMCA accomodation. Saying that so, imagine what happens on the rest of the ship: lines everywhere, bad service and even very angry personal doing guest services everywhere, even in the areas where you have to pay extra to get a relative decent service like the spa. The food is awful, the venues are imposible to be there, the pool area is horrible and you cannot find a place anywhere just, but just to sit down to do anything. So why pay 1700 USD per person for a trip that you are not going to even enjoy but also you would not be able to use the facilities or eat decently.
So if you think "what the heck I'll give Costa a try", please don't do it even if the ports are going to be the most wonderfull ones in your life: just stay at home.