We (the Aussie girls) did the Rhine River Cruise recently & loved it.
The crew were great & our cruise director worked tirelessly throughout the cruise.
We had to change ships (VE to Gefyon) in the middle of the cruise due to water levels.
Wasn't looking forward to that but it was so well organised you would hardly know you changed ships apart from the packing & unpacking. We were compensated for that by Viking taking all the guests to the music performance in Vienna which was wonderful.
Overall we had a great time & met some lovely people.