We were 5 of the 48 Americans on Board (out of 3500 total on board) and we never met another one during the 8 days. So if you're going with the expectation of meeting people or socializing, get cozy with the cabin stewards (who speak English well), or learn Italian. No attempt was made to introduce us to any of the other English speakers.
If you've traveled around Spain, France, and Italy, you know that people don't "queue" like they do in the UK and the US. Generally, people crowd around a counter and let "survival of the fittest" rule. Not a complaint, just the way it is. You have to decide for yourself if you want to be on a ship with 2000 passengers who don't like to wait in line. Also, leave your sense of personal space behind. I move through a buffet line pretty quickly, but I still had people close enough to be sharing my clothes and breathing down my neck. My advice is to get to the buffet at least 30 minutes before the crowd hits, and everyone seems to behave themselves. I wouldn't wish noon at the buffet on anyone.
Dinner is more relaxing, with decent food served lukewarm. I'm not sure how long in advance the food was prepared. Main courses were generally competent, but the appetizers were hit or miss generally miss. Pasta courses are excellent. Desserts were definitely phoned-in. Their idea of a "sundae" is a scoop of ice cream with a cracker in it. I give them full marks for being able to recycle the same ingredients night after night with different descriptions. Which is the real problem with the food You just get sick of eating the same things after a few days.
Smoke is everywhere, but you get used to it. Then again if smoke is a problem, don't vacation in Europe.
Costa tries to make back their money on beverages. They are constantly selling booklets of tickets for (a) water (b) coffee (c) non-alcoholic beverages (d) wine. Those are all separate booklets. The plan seems to be to get you to buy these booklets and hope that you (1) don't use them all, or (2) forget to have them on your person at all times. More than once, I had to run back to the room to get the tickets so my kids could get juice at dinner. Once, they gave out free soft drinks for 30 minutes, and listed it as an "event" on the daily calendar.
You will also get your picture taken a lot on the cruise. They are hoping you will spend 15 euro to buy it after it is posted on the wall in the main lounge. For example, you will get your picture taken every time you leave the boat, during the lifeboat drill, just about every night at dinner, etc.
Cabins are huge and comfortable. Great shower. Lots of room for clothes. Ugly, ugly, ugly decor. It amazes me that they built the ship in 2007 and chose the "Miami Vice" color scheme.
Cabin Service is outstanding. Even when my kids trashed a room, they cleaned it up perfectly. Costa hires a lot of non-Europeans for the service work, and they are the stars of the show. The American and European staff is mediocre, and I generally had the feeling they'd rather be somewhere else.
Embarkation took forever. Disembarking was a disorganized mess (but exciting: Will I get my passport back?).
As for kids on the cruise, they loved it. This is an inexpensive family cruise line, and you should expect to see a lot of families and kids. If seeing kids bothers you (as it apparently does from reading the reviews), go on an expensive cruise somewhere else.
My expectations were low going into this vacation, and they were met. The saving grace of the cruise is that my kids loved it. Basically, there are parts of a cruise even Costa can't mess up the excitement of being on a big ship, visiting exotic locations, and spending a lot of time with family.
All in all, this is a *perfect* cruise for kids, and it is something you would do *for* your kids. In fact, the whole experience was like spending 8 days at Disneyland take that as you will.