Come in with an open mind. It is a cruise. But it is not going to be what you have experienced with Cunard. (I’m basing this on my perception of Cunard as being rather formal.). I am usually a Disney cruiser (but also sailed Princess, NCL, Royal, MSC and Carnival - all but Princess just once so far). I am scheduled for second cruises on MSC and Royal next month.
MSC has a reputation of poor shoreside customer service - but a much better ship experience.
I have not sailed Yacht Club (YC) on MSC, but find nearly all reports of it as an excellent experience.
Consider what you like to do on a cruise and ask more directed questions if you would like further information (as above poster suggested). Also, if you know ship, cabin category, or itinerary, responders can address your queries more appropriately. (I could tell you about MDRs or the buffet, but if you are going to experience YC dining exclusively, that area gets addressed a lot; as does the excellent assistance typically provided by the butlers).
Do you want to know about the main theater shows?
Live Music?
Pool?
Spa?
The conversation has begun…