We cruised the Viking Odin in September 2012 on the Danube from Nuremberg to Budapest. The cruise took us to places we had wanted to see. Our room was comfortable and well kept by housekeeping, the ship was very nice and the staff was very good especially the Cruise Director Joe, the front desk personnel and the hotel manager. The dining room staff was very attentive.
The daily excursions gave you an overview and we used receivers connected to the guide -- an excellent tool. For the most part the on-shore guides were knowledgeable and interesting. The 4 or 5 additional excursions could not be signed up for in advance of the cruise but these were quite good especially the Mozart-Strauss concert and the Danube Gorge. Why was the sign up not offered prior to sailing is a mystery.
Dinners in the Main Dining room were extremely noisy because all 190 guests were present at the same time making it difficult to have conversation. The dining room was crowded with armchairs that made it difficult to get in and out. Food was good but not exceptional. We did not purchase the wine & spirits package because wine or beer was provided at lunch and dinner and while it was built into the cost of the cruise, it was not worth it. We (6 of us) would have preferred to pay as you go instead. The evening entertainment consisted of a few local performers or a lecture by one of the staff, and there really was no space on board for much of anything. We were often linked up with 2 or 3 other Viking vessels visiting the same cities and used each other for transit to shore.
Viking's book about the trip was most informative but they did not need to spend money on a small leather bag to hold it and 2 name tags that hardly anyone wore. Viking's marketing is quite extensive and the patrons are paying for it rather than getting value for their money on the trip.
Overall, the cost was high when you compare this with a high quality but small ocean going cruise ships. The only value with these river cruisers is that they can get into places where a small Ocean going vessel cannot go. However, the cost of this access and the marketing - $3 to 4k more than a small ocean going cruise line like Oceania - causes me to think that the trip was not worth the cost.