We have cruised MSC after only cruising on Disney prior and afterward. It's definitely a different product than Disney, but they are a family friendly cruise line. Their idea of customer service is very different from Disney's, but, it was still a good experience for us. We had some issues (room assignment) that were difficult to resolve, but that is partly because we are a larger family that books different types of rooms and we booked the Seaside when it hadn't been completed yet. My parents and others that have sailed with us haven't had the same issues.
My kids enjoyed their kids clubs. It may have been because we sail at off times, but some of the activities in the clubs didn't actually happen when they were supposed to happen, partly because there were not enough children to do the activity. The clubs are not open all of the time. They take the kids around the ship (for parades, to dinner, to the shows, 4D cinema). They have their own characters (Doremi, Mila, and a few others). My kids still sing the Doremi song sometimes.
Outside of the kids clubs, they don't have as many activities as Disney. They have trivia, bingo, dance lessons, pool games, crafts, and other activities. There might be one activity going on at a time where Disney would have four or five.
There shows are very different from Disney's shows. Their shows are more cirque du soleil. Each night is kind of a different variation with similar types of acts. Some were more entertaining than others for our family.
Many people complain about the food. We didn't have a problem with it. Their steaks (which I don't eat), I've heard/read are not really great. Their pizza is great! Their other food was good too. Some of my family members prefer MSC food to Disney food.
Their clientele is more international than Disney's. By this I mean, if you are from the US or Canada, you will be in the minority, most likely. They will often make announcements in several languages. It wasn't really an issue for us, but English was not the first language for most of the kids in the clubs.
You might want to take a look at the MSC forum on cruisecritic. I think you will get a more balanced view of MSC there.
Overall, if you go in realizing that it won't be the same as Disney, you can have a great experience. Their ships are clean. Their food and entertainment were good (at least what I ate/saw). You will probably miss some of the things from a
Disney cruise, but you definitely can have a good experience.