My wife and I recently completed a cruise on Harmony Of The Seas and it is indeed a beautiful ship. This was our 8th Royal Caribbean cruise and they continue to impress with the new features everytime we board.
The slides were a nice addition to what is essentially a clone of the Oasis and Allure. If you decide to try the Abyss slide make sure to keep your elbows tucked in and your knees straight otherwise you can receive some nasty brush burns.
The shows were very good including Grease and both of the shows in the Aqua theater. The ice show "1887" was fantastic also. The only thing about these shows is you need reservations beforehand or you risk not getting in to see them.
Nice cabin with enough receptacles for our needs. Shower and bathroom typically small. Bed was very comfortable.