My wife and I recently went on MSC's cruise of the eastern Mediterranean. While overall it was a great experience, there are a couple of things that everyone should know about MSC prior to booking with MSC. First, be prepared for long lines. Our initial boarding took about an hour and was extremely confusing. There were no signs directing us where to go and communicating with MSC greeters was difficult as most spoke very limited English. Anytime that you are getting off the ship, be prepared to wait. MSC does not understand how to stagger everyone disembarking from the ship so you will be crowded into the ladderway with 4000+ passengers like a can of sardines as everyone tries to get off.
I will say that the food on MSC is mediocre at best and often just outright terrible. Of all the meals, dinner was done fairly well, but lunch and breakfast were poor. Unless you catch the buffet at an off hour, it tends to be really crowded. The options are fairly poor (i.e. cold cuts, tiny pancakes, greasy hash-browns for breakfast), and I couldn't find a single spoon anywhere. If you elect to go to the restaurant instead of the buffet, be prepared to wait a long time for your food and deal with servers that don't speak English well.
Though the cruise seems cheap at booking, get ready to pay a lot with drink packages and excursions. I had no idea what the drink packages were until they forced me to make an impulse decision as I was checking in. I elected to take the Alegrissimo package, which was unlimited drinks and often had trouble making this package worth my while. One note, when they say draft beers, all they have is Heiniken and Amstel Light (and maybe Strongbow and New Castle if you're lucky), so don't expect to find more draft beer.
Kids run a muck everywhere on this ship. This seems to be a more family oriented cruise, which is fine if that's what you're looking for, but if you're on your honeymoon or a romantic vacation like we were, this is really annoying.
Now on to the good. The cruise ship is amazing. They did a fantastic job keeping it clean and keeping my room clean. The cleaning lady responsible for my room cleaned it twice a day and was like a ghost. The excursions were awesome. I honestly did not have one bad tour guide anywhere we went, and the destinations were a lot of fun. The entertainment on board was phenomenal. They kept each show to about thirty minutes, which was long enough to keep me from getting bored. Most of the lounges were really nice and classy. The workout area was great. There were about 7-8 treadmills with some bike machines and elypticals plus some free weights, machines and mats to do yoga and whatnot.
Overall, I would say that the good outweighed the bad with this cruise line, but if you go with MSC, be aware of these issues upfront.