Lived through my first cruise, a 14 day tour around the main island of Japan. It included a stop in Busan, apparently due to international maritime law requiring a 2-country itinerary in many countries.
Ship: new and beautiful. Silverseas Nova, just one year old.
Best room: The fore of the 10th, top enclosed, level.
Everything about it was great, except the food, which was mediocre, despite it being a high-end luxury line. All rooms had a deck with comfortable patio furniture, which was a must have amenity, imo. The rooms were spacious and comfortable; even the water pressure and shower exceeded expectations. Another pleasant surprise: No annoying fellow passengers, in particular, nor as a mass. I'd say the nationality of the passengers was equally split among Americans, Brits, Aussies and Spanish.
It was a cruise of Japan which both enhanced and detracted from the itinerary. We were able to visit beautiful, enticing, far-flung cities in a highly convenient and luxurious manner with a minimum of effort on our part. On the other hand, the food served onboard paled in comparison to what one can find in a Japanese food court, let alone at an expensive restaurant. The toilets on the mainland, even at most train stations and shopping malls, were also an upgrade over what was furnished on the ship, which was basically an ordinary commode; I didn't expect to think about planning my shitting schedule around shore excursions. IYKYK. The onboard entertainment was nothing I'd seek out on my own. On a cost per-day basis, one could easily travel Japan to the same or similar cities and save bundles.
It was a unique and likely one-time experience. There were many cruise enthusiasts on board. I don't get the attraction unless one is mobility limited, or strongly against navigating airports and train stations on their own. Also I imagine certain itineraries are much more difficult to recreate without the benefit of a ship. However I'd prefer to visit fewer locales or simply stay in one place. Although as a way to "scout" Japan and see where I might want to return it was great.