Symphony of the Seas is a virtual carbon copy of the Oasis of the Seas which we sailed on in 2011. So we knew we would enjoy the boat. It is hard to believe you are on a ship and not at a luxury resort complex.
The ports for us were of little consequence, this was a winter getaway. The only new port for us was St. Kitts and we enjoyed it. We took the Brimstone Fort and Fairfield House excursion and it was pleasant and worth it. St. Thomas is kind of a nothing port to us. We took an excursion in 2011 to Magen's Bay which is scenic but crowded. The rest of the island is pretty much squalor. Nassau was better than in 2011 when it was chaotic and a little uncomfortable. It is now better looking and organized. With 5 ships in port there were 20,000 potential cruisers, so it was also quite crowded, but not unpleasantly so.
Our cabin on deck 11 was great as was our cabin steward Estuardo. Be prepared to do a lot of walking to everything, this ship is huge. One beef is the intentional slow elevator service. They just take forever to come and it is not because of the crowds. I say intentional because the other elevators in the bank are not moving even though you called for one. They must only run a few at a time based on some algorithm. Not a customer friendly idea. One other thing to note, when you enter your cabin you must insert your cruise card in the slot by the door and leave it there to activate the lights. If you don't, you will have no lights. Which is fine, but how about a sign telling you that.