I’ve posted other comments, so no need to repeat myself, but in short I thoroughly enjoyed MSC (June 2009 in the Baltic).
Of course every ship is different, but here are my specific comments: Movies were free. Cabins were fine (it’s a ship – shipboard cabins are always small unless you spring for a suite). The bath had 2 washcloths, and the chambermaid would bring as many more as you wanted. The chambermaid and her assistant were very accessible and most helpful. If not in sight they responded quickly to a phone call. I wouldn’t bother with room service – you can go to the buffet and simply bring it back to your room. The buffet is open most of the day, to 5 pm. The MSC Opera cleaned its windows every day while at sea. Any salt spray we saw was fresh (we saw it go on, and we saw it cleaned off). Dinner was marvellous, served quickly, and not lukewarm. The restaurant service was consistently excellent. Amazing excellent, I’d say, especially considering how busy they were. Pizza is free, from noon to 5 pm; and it’s amongst the best pizza I ever had. (Note that it’s Italian pizza, not Domino’s or Pizza Hut.) All the elevators worked. We’re non-smokers and had no discomfort whatsoever. In sum: we travel a lot, and the MSC Opera was a wonderful 'hotel', especially the service -- the staff were exceptionally friendly, responsive, and helpful.
Overall advice: ENJOY your holiday.