Ah, I'm jealous!
Never on MSC line. But I have been on a couple and I'd offer this:
(1). It's a lot of fun. But remember, you need to bring the party too. It's just like a bar or club. If you go expecting to "be entertained," you might be let down. Drink, swim, gamble, and just do all the stupid stuff. It's kind of corny at times, but still fun haha.
(2). I don't know if you have any ports, or how many, but I always find the "ports" as fun as the ship. Time is usually short (I think 6 to 12 hours generally). Definitely rent a car if it's offered (it'll be offered, literally, feet from the port exit by a third-party not affiliated with the cruise line) and you or the driver is SOBER. Do not get locked up abroad haha. But it allows you to see non "touristy" parts you'd otherwise not get to venture to. I remember jet skiing at one port and laying on the beach, and another port we rented a car, drove through (perhaps a dangerous, in hindsight) one-lane road through a jungle and rode horses to some ruins.
(3). WATCH YOUR VALUABLES. This applies mainly to women, but men sometimes like to flash their rings, watches, etc too. My mom was talking and bartering with a, seemingly, friendly local, and he admired her bracelet. 10 minutes later after she'd purchased a few items and was walking back to the ship she realized her diamond bracelet had been lifted. Of course she couldn't PROVE it was him, so all we could do was go back and politely ask. Of course they said 'no', and snickered as we left. It's nothing against "the locals," just be wise. Don't take valuables on the trip, period. And if you do, keep them in the safe while in port. Do not walk into "touristy" areas with valuables.
(4). I'm jealous, have fun!