I have cruised on many different cruise lines since my first cruise back in 1996, including 5 star and budget ships.
This is my first time on Costa although I have sailed on their sister company Carnival and many things about the management and layout of the ships is similar.
Check in at Barcelona was very efficient as Costa pick up and drop off at all the ports on their itinerary so you don't get the long queues and congestion often associated with the single port of departure style of cruise.
The cabin was a good size and clean - cabin staff were slow at cleaning (I think mainly because of the embarkation routine at every port meaning the cabins of guests not leaving/joining the ship were always the last to be cleaned.
Toiletries in the shower and tissues were not replenished - so we bought shampoo and shower gel and tissues (more of a minor irritation than anything else).