2Fltravelers (see above) have written extensively about this cruise. They should be praised for their level of detail.
If you are expecting Crystal Cruises or Oceania or the Queen Mary 2, please book a different cruise. The Marguerite has everything that you could hope for in a small, river-going vessel. What--no big-named comedian or a stage show re-creation of "Phantom"? You'll be too exhausted at night to do anything but collapse into the pool (which is bigger than you'd expect for a ship of this size).
Sure--the food is made so that it doesn't upset anyone, so use the "action station" to try something new at lunch and don't be afraid of the little red chilis. For the most part, we stuck to fish, chicken and lots of vegetables and fruits--if you do, you'll be happy.
Ama Waterways does go to some places that other ships do not. These small towns are well worth visiting--much more so than Hanoi or Ho Chi Minh City (although these metropolises have interesting sites, even if not so charming).
For convenience sake, you'll be grouped into cohorts and assigned a color. You may or may not like everyone in your cohort (with whom you'll spend time on buses and tours), but--hey--it's not the end of the world. And you're bound to find others on the cruise who may be more to your liking. Don't sweat the small stuff--the guides and cruise director and bus drivers and cabin attendants and servers are all knocking themselves out for you--even if they don't completely understand your need for gluten-free, lo-cal shade-grown coffee picked by Bhutanese virgins during the new moon cycle.
Short of carrying you in a sedan chair with Nubian slaves waving palm leaves at you, everyone working on or around the ship is trying to make your cruise a pleasant one. Where else could you dress up in traditional costumes and dance to "YMCA" in the middle of the Mekong River?
Smile. Be kind. You'll sweat a lot--so what? Enjoy the local wines and spirits. Eat a tarantula leg or a baby octopus. They won't kill you and you'll have great stories to tell later.
Oh--and if Asiana Airlines offers you the "tourist hotel" for your 8-hour layover in Seoul, skip it. By the time we figured out how the shower worked, the water jets shot my wife up over the DMZ where she was tracked by North Korean radar. Stay at the airport and enjoy the Business or First Class lounges; or try the free showers on the 4th level.
And, yes, you can buy anything you would ever need in Vietnam within 2 blocks of your hotel. It's cheaper to buy underwear and shirts and them hand them out to locals at the end of the cruise than it is to launder what you brought with you. And please think twice about taking pictures of the "adorable orphans" at the schools that Ama Waterways supports--these children are not in a zoo. Let them sing for you, buy a postcard or two and promise to make a donation when you get home (and then keep your promise).
Have a great time!
Most of all, have fun.