I am with Marc. Asia is a wonderful cruise destination. So many of the ports are easily accessible and the cities are wonderful. The new cruise center in Singapore is rapidly expanding and is a great city for those a "first time" visit to Asia. Singapore is clean, safe and interesting. It isn't my favorite city in Asia but it is very tourist friendly.
We did a two week cruise from Singapore to Hong Kong in December with three days pre-cruise in Singapore and three days, post cruise, in Hong Kong. Destinations like Ho Chi Minh City and Ha Long Bay were interesting, beautiful and the people were quite friendly.
The best part for us is the food. The local restaurants and street vendors offer a variety of delicious and interesting foods that you will find nowhere else in the world. The "Hawker Centers" in Singapore will offer you the widest variety of foods in a clean and well managed area. The liver and gizzards I had at the Market Street Center in Singapore will go down as one of the best things I've ever ate. Don't worry there is infinite more and less "ofal" things at the Hawker Centers. BBQ duck, chicken rice, BBQ pork, just to name a few. The meals we ate at the Hawker Stalls were equal or much better than at the "expensive" restaurants. The "ambiance" was better at the restaurants but the food wasn't. Also, Singapore is not a "cheap" city.
You will find that Vietnam is still communist but it has embraced Capitalism in a big way. In Saigon you will see everything from Gucci, Prada and Armani stores to large open air markets. A shop-a-holics dream.
I will be very happy if the U.S. cruise lines base more ships out of Asia. It is truly a unique destination and one that travelers will appreciate.