We really enjoyed our Christmas Market Cruise on the Danube. We are planning to book for the Rhine Christmas Market Cruise next year as well.
Our family of three (myself, husband and 12 year old son), found the cruise to be quite enjoyable. We had a suite and a AA room diagonally across the hall for our son. The suite layout is different than in the brochure and online. This was a bit off-putting at first, but it ended up working out ok. There is less space in the living room area since they have made the balcony larger. This eliminates the sofa in the room. We did find that you really needed to use the bed for relaxing. The two small chairs in the entry were always in the way so we moved one to the desk area and the other by the bed in the corner. Our son's room had plenty of space.
The rooms were quite comfortable and well maintained. We had a large bathtub in our bathroom, but we did not use it. The shower with multi shower heads was nice.
We did participate in some of the tours (Melk, Budapest, part of Salzburg), but we found it much more fun when we went out on our own. The guides were all nice and knowledgeable, but sometimes as a family we like to see more or different things than what are offered. In Vienna, we took a carriage ride, shopped, and went to the Dremel chocolate place as well went to Schonbrun Palace.
I get quite seasick on typical cruises. I had no issues with a river cruise. The cruise was highly relaxing, we loved reading and watching the world go by as we sailed up the Danube.
The food was mostly very good. The standout for us was shepherd's pie for lunch. It was the best we'd ever tasted. Out omelets at breakfast were quite good. The only food complaint was that it is impossible to get a meal or a snack outside of tea, breakfast, lunch or dinner. There were times we weren't hungry for a big dinner, but knew if we got hungry later we would be out of luck. The bar should offer sandwiches or something simple with the drinks for a small cost. There are simple offerings at lunch and dinner in you don't like the set menu (minute steak, chicken sandwich, french fries, etc.). I would be nice if you could get those things outside of meal times for a fee. Our server was terrific. In fact, we loved all of the staff.