Just finished Viking Romantic Danube cruise. First time this Viking ship sailed, without interruption, from Nuremberg to Budapest. Only, maybe, the second week that any Viking ship made the cruise end-to-end without a ship swap. The low water levels on both the Rhine and Danube will likely continue into 2019 season (begins in March).
The cruise, when uninterrupted like ours, was great. Crew was great, very good customer service. Ship was in great shape. However, crew members did say it has been a very tough season - with all the ship swaps and motor coach substitutions, most of the "cruises" were filled with very disgruntled customers. This cruise and crew would entice me to take another Viking cruise.
However, I plan to do even more due diligence before the next cruise.