Just back from my first Costa (have done Cunard, Princess, HAL, RCCL, Carnival before). Deliziosa is a new ship and a such was in excellent condition.
Embarcation at Copenhagen was painfully slow. They had only 2 desks, manned by ship's dancers who only had to check name on embarcation form you carried with your passport. No computer terminal or even a printed list to tick names. Still took them for ever. I stood in a queue for 1 hr 25 mins. An elderly lady behind me fainted, and I'd be surprised if she was the only one that day. Costa Card (combined room key/on board charge card) was in the cabin.
Plenty of storage space in cabin, cabin steward excellent with high standards and desire to help when needed, cabin tv channels not good unless you speak Italian, French, German, Spanish. Only English-speaking channel was BBC World.
Whole ship was very clean, most staff speak reasonable English, announcements were made in 5 languages but I got used to that and would just switch my ears off after hearing the first one I understood. Evening shows were ok - the multi-lingual ventriloquist (sounds painful) was a scream and I literally cried laughing.
Excursions expensive but I do my own thing anyway - you can find everything there is to know and see about your destinations on line and don't have to spend a fortune on ship's tours.
Food - well, compared to other lines it was disappointing. Buffet at lunchtime was ok, but nice to have waiter service in main restaurant at lunchtime if you're not ashore. It's open dining then so you can go when you want between 12 - 1.30 and don't have to sit at your assigned dinner table. Evening buffet not good, unless you like pizza. All they have is pizza, one pasta dish, one fish that to me screamed 'school dinners fish' and when I was there, the meat option was luncheon meat. Restaurant dinner menu disappointing but you can always get salmon or steak if you don't like that evening's menu. Hazlenut ice cream - now that really was Deliziosa. Room Service continental breakfast was ok and no extra charge. If you want RS any other time there's a 2 Euro charge. They don't do room service for lunch or dinner - I guess they're busy in the restaurant.
Drinks very expensive. Even the Cocktail of the Day was 5 Euros which gets to almost 6 by the time they add the service charge and I don't think £5 for the day's cheap cocktail is particularly cheap. I'd gone on a last minute super-cheapie and had no budget for many extras, so stuck to normal water at dinner and didn't suffer from it. You can always get tea (lots of choice of fruit, herbal, normal, etc)or coffee in the lido buffet up to 11pm.
Several bars to relax in, but none for peaceful relaxation as they all have some sort of live music in the evening.
Casino - only takes your Costa Card, not cash, inc. the slots, so restraint needed there. Can get a bit smokey.
There are smoking areas in the bars and one side of the pools.
Less than half those dining had dressed to the "Gala" dress code on both those nights, so if you don't want to take fancy clothes you won't feel out of place.
Internet's expensive but before I went I'd googled free wifi and found plenty of places I could use their computers (usually public libraries) or my netbook wifi for free. Some places you could get on line just off the ship - watch for where the crew go - when you see lots of Filipinos at their laptops, chances are there's free wifi.
Would I go Costa again? If I got a good deal like this one (under £350 for balcony cabin for sole occupancy for a week including flights), Yes.