There are a lot of negative reviews about Viking River cruises on other sites as well - Trustpilot for example. What is very clear is that the average rating on all sites for Viking has fallen significantly since Covid. Some of that is down to the voucher and vaccination requirement issues, but there are a lot more general poor reviews, often re situations where Viking could have been much more helpful, without really costing themselves any money.
We went on the Grand European tour last autumn and counted ourselves as very lucky that we got through the Rhine Gorge on the ship - sailings before and a week later couldn’t get through and bussing was necessary. However, we had to do one ship change at Regensburg and that meant we ended on a ship with noticeably poorer service and crew experience than the original. If we had wanted to, we could have added to the poor reviews.
The problem Viking ( and other lines) have is that increasingly water levels are too high or too low to sail the entire route. This means a lot of cruises have an element of bussing. Add that to the crowded nature of the moorings where ships are tied up side by side and so you cannot use a balcony. You can see why passengers get upset. No cruise line wants to deter passengers, but the more this goes on and they don’t point out how often it happens, the more they will have bad press. This will put off those who research the cruises from booking and mean unsatisfied clients from those who do go.
Often they do not know until the cruise is underway whether they will get through. A couple of days rain can change the water level quickly. Once you are on board, however, they could make a much better job of explaining the situation to passengers and telling them what is likely to happen. We knew as we looked at the Rhine water levels on a website that showed forecast base on existing and likely rainfall.
one other point - on the Grand European Cruise, the ship sails for around 4 to 5 days with the sun deck out of use - the bridges on the canal are so low even the ships bridge has to be on scissors and lowered for each bridge to get under the parapet. We knew that, but a lot of passengers didn’t and were upset about it. It’s a fact of that waterway and really should be made clear on the publicity and schedule for the cruise - but Viking hope people will simply accept it.