I sailed on the Harmony of the Seas with my wife and two teen daughters (ages 15 and 14) for Spring Break on 4/8/17. We loved it!
Had an excellent trip and went on amazing excursions (kayaking and zip lining in Labadee, horseback riding in the ocean and climbing Dunn's River Falls in Falmouth/Ocho Rios, and dune buggying in Cozumel).
The ship may be the largest in the world, but it is also the best. We never felt like it was crowded. The food, entertainment (don't miss the Fine Line in the Aqua Theater), and cabins were all great . Endless options of on board activities for individuals and families of all ages.
Interior cabins were roomy and clean. We were close to the elevators, so it was very convenient.