I went on this ship as a teenager and had previously been on two Disney cruises. I love Disney cruises! They have everything you get with other cruises, plus interactions with the Disney characters and that extra Disney magic.
I traveled pretty soon after the ship stared, so some of these problems may be fixed, but the waiters I had on this ship weren't as fun, helpful, or personal as the service on the other trips.
Also I could tell it was a bigger ship was bigger and it felt more crowded. Maybe this is just me personally, but I preferred the smaller cruises (Wishes and Magic)
It goes without saying that DISNEY's cruises have a lot of activities for kids and families. This is their target audience and they excel at it. They have so many fun activities. The children's play area is one of the funnest places I've ever been. All that said Disney really tries hard to have things for teens, "tweens", and adults. The teen area was really cool and they had a lot of really fun activities. However, most of the people there were rich teens who thought they were too cool for everything and spent all there time there avoiding their families. They were disrespectful to the staff and tried to ruin the activities. After a few attempts to hang out with the teenagers a gave up and just hung out by the pool and did the family activities. If you are going with a teenager who wants to spend time with their family, likes Disney, and wants to have fun, they'll enjoy the cruise but maybe not the parts geared to teens. If your teen just wants to spend time with people their own age, they can lock themselves in the teen area and avoid the rest of the family, although you might want to consider another vacation.
I've most just explained the negatives but I can assure you the cruise was super nice and so much fun. I would do it again and again and in fact would recommend taking a 7 night or longer cruise.