This was our sixth river cruise; fifth on Viking. So, we were pretty familiar with the Viking experience. The Viking longships are beautiful! The cabins are roomy and very functional; complete with heated bathroom floors and the best shower I've seen on a cruise ship. The food is very good, and service is excellent. We were in cabin 334 (French balcony).
Nick, our cruise director, was the best cruise director we've ever encountered in the many river and ocean cruises we have taken!! He was friendly, accommodating, patient, and showed great humor (and restraint) when problems arose. From now on, he is the "bar" by which I will evaluate other cruise directors.
We did both a pre-cruise trip (Amsterdam) and post-cruise (Basel); both were very good. The on-site Viking reps were friendly and knowledgeable and made our transitions seamless. Same thing for the transfers to and from the ship. We particularly enjoyed the included walking tours in Amsterdam and Basel. In Amsterdam, my husband and I visited the Anne Frank House, which was very moving. In Basel, we did a ferry ride across the Rhine (recommended by the on-site Viking rep) and visited a few museums. Basel is small, but charming. Two days in Basel were enough; I would have enjoyed 1-2 additional days in Amsterdam.
We visited the Marksburg Castle; not sure if it was in Koblenz.