My review is from perspective an American who has been on several other Royal Caribbean cruises. I was surprised that only about 5% of the passengers were from the US; my experience with the earlier cruises was that the majority of passengers were Americans even for cruises in Europe.
In any case, the time on the cruise ship a lot like being in Britain, which certainly was an interesting change of pace. I especially enjoyed the British tea (not Lipton) and Guinness on tap.
Embarkation: We took a National Express bus from Heathrow to Southampton after an overnight flight from the US and then spent a night at a B&B before the cruise. Boarding was smooth although we were surprised to receive an email with boarding times based on deck level. The lowest decks were not supposed to board until a little over an hour before the scheduled departure. Fortunately we cruised enough times that we were allowed to board earlier.
Had great seafood lunch near the lower cable car stop.
Beautiful city in the greenest part of Spain.
Convenient bus and train service to London and Heathrow. Worth a visit if you have time.