Cities on the list I've been to:
Charleston, SC - Kind of a weird inclusion to me, interesting historical city, some good food, very hot in summer (duh). We'll go back sometime, but it's not a place either of us dream of going.
Barcelona - Yeah, one of our favorite cities in Europe, very walkable, nice beaches, good food, interesting sites. Good.
Rome - Only there for a day, my wife wants to go back for several, I think it would be great too.
Seoul - I liked it a lot, my wife preferred Tokyo, massive city, we had some good food, stayed at a great hotel, not that much real history since the place was bombed out in the war.
Tokyo - Interesting, we had a great walking tour of 8 hours that was exhausting but interesting. Massive city of course, the rail transit was confusing but our guide did it for us. Also bombed out in 1945.
Istanbul - Looks interesting "pn paper", we're going in September for 8 days.