This cruise from Nurnberg to Budapest was threatened to not take to water due to the low water levels on the Danube in the late fall of 2011. Fortunately rains fell the week before we were to cruise, though Viking cruise line's carefully worded information seemed to threaten that whether one cruised or not was the chance one takes upon booking??? That should have been due warning about the integrity of the Line, but it took more bumps to really recognize the lack of quality on this line.
The food was poor. Despite the assertion that local foods and recipes would be featured we found it impossible to get a soft-boiled egg at breakfast, the cheese selection was very poor, no brotchen, no schwarzbrot, and the coffee was weak (more Norwegian-American) than European or Starbuck's. Generally however, breakfast was the best meal. Dinner was 4 courses. The salad was always a joke. The entree was only acceptable if one ordered the standard menu of steak/chicken/salmon and baked potato, but how local is that? The soup was never piping hot, and I believe it may have been the cause of sickness on the ship. Many cruisers were sick on this boat. Staff were sick too. I have never been so violently sick for so many successive hours. Generally I am a very healthy person. I think the kitchen and cook need to be replaced. The serving staff varied from competent to surly. The house wine was drinkable, free, and flowed with dinner.
The outings at each port were accompanied by knowledgeable guides. I was unable to make every outing due to sickness and am generalizing here. The hotel staff were attentive and had to do extra cleanup due to sickness to be sure.
If you know Europe at all, you are better off on your own along the Danube. You can eat better and stay better for less than half the price and a little internet research will guide your historical/architectural quests quite sufficiently.