We have been on many cruises and have travelled extensively through Europe. We found the staff on the Viking Kara exceptional. The itineraries were interesting with planned tours and optional ones. If you do take this itinerary make sure you do the pub crawl in Cologne, we loved it.
Our only disappointment was missing out on the windmills tour, a bad storm moved in and the tours had to be cancelled. Certainly not Viking's fault but still a bit of a disappointment.
The tour through the Rhine castle region was magnificent and we were blessed with good weather for that.