We really thought the Viking longship was built just right with its very convenient and pleasant public areas and restaurants. The service was excellent. The staterooms were kept extremely clean and our AA Suite with its separate living room was worth the substantial extra charge.
The Danube itinerary, which we had done on Viking a few years ago, is excellent. However, while docked you are frequently tied up to other Viking boats and have no view while in port.
While mid-trip we were forced to switch from another Viking longship due to low water conditions (which of course Viking cannot help), the switch was accomplished very efficiently with a 3 hour bus trip. The Tour Director "Leonard" was simply excellent the entire trip not just in the transfer.
However, the food while offering various options was so disappointing and mediocre at best. We are used to very good and often excellent food served on ocean going ships. Perhaps Viking is providing that on its new ocean going ships, but we will not book another Viking riverboat cruise.