We liked the route starting with two days in Paris and ending with two days in Prague. In between we cruised the beautiful Main, Moselle and Rhine rivers. For North Americans I would recommend arriving a day early to recover from jet lag. Every day on the boat we stopped at a small town that was invariably picturesque and very old where we were met by a local guide to show us around.
The rivers traveled along were fairly narrow so there were always things to see while cruising. We had seen Viking ads on tv and liked the look of the boat, we really didn't want to cruise with a large number of people.
The staff/crew were, without exception, extremely friendly. The head guide really made the trip memorable. He was very knowledgeable with a nice sense of humor. Viking's organization throughout our holiday couldn't be faulted.
The cabin was kept spotless and was beautifully finished. I really liked the heated bathroom floor. Although our cabin was right at the rear of the boat we barely heard any noise from the boat's engines.