I am biased as I live in Bangkok. This trip wasn't the best time to visit because of the terrible flooding but those who ventured ashore were well rewarded. One couple took the excursion to Angkor Wat in Cambodia and rejoined the ship in Ho Chi Minh. This would have been my choice if I was a first timer.
Everyone's favourite city and a favourite of mine as well. The Star Ferry is a must and you won't get anything cheaper or more spectacular than the Hong Kong skyline from the Ferry. Up to Victoria Peak by cable car is also a great experience.
the "Home Port" of the Diamond Princess as it was built here. The tourist authorities actually love having the ship berth and there were all sorts of displays and stores port side. Nagasaki is a wonderful city for reflection at the terrible damage done at the end of WW2.