Vantaggi
The pay is great. You might only make in 40's your first year, especially if you have no Coast Guard credentials, but once you do you can make some a decent paycheck. There's a lot of port calls. I frequented the Mediterranean, Persian Gulf, and Pacific.
Svantaggi
I'd really only recommend MSC to someone really young, or the retired. But be prepared to give up 9 months out of the year to the sea. Also, unlike real shipping companies, it can be pretty hard to get a relief. If you're doing something specialized, I was a Search and Rescue Swimmer on top of AB, it can be even more difficult. But at least anything that inconveniences you leads to monitory compensation, including not getting a relief, not having your own room on the ship, air conditioning broken...