We have enjoyed our varied ocean cruises and tried river cruising as a change.
We lucked out the weather was perfect every day -- we avoided the floods from a month earlier and we also lucked out on missing any lock closures due to a strike in Germany,
We did the pre-cruise option in Prague. We loved Prague, and actually booked a room a extra day at the beginning on our own. We found a tour agency to pick us up from the airport and take us on a day trip the following day. We found them on Trip Advisor. Mike's picked us up from the airport and privatePrague Tours took us to Cesky Krumlov. The both were great. The 1/2 day tour that Viking arranged the following day was also good. I would suggest visiting Prague but doing it on your own. The value (one short tour and the trip down to the boat) isn't there. it would be easy enough to arrange this on your own.
We splurged for the Explorer suite. We really like the extra room, and the beginning when the top is closed due to bridges it was nice to have the balcony. Please note these are much smaller than they appear in the pictures. Still we enjoyed the room. The staff were very good. We did a lot on our own (we were a tad younger -- in our 50's) than the rest of the people so we seemed to have more adventurous spirit than some. I suggest if you do this to as your tour guides for things to do or look it up ahead of time. Our connoisseur on the Njord was helpful but not as knowledgeable as the local people.
Dining was adequate -- not overboard like on ocean cruises -- I liked this. We walked between 6 and 14 miles a day (I carried a pedometer) The longer walks were in Prague. This is probably much over the norm. We wanted to do everything.
We loved Passau, wished we had more time in Melk. The tours were perfect -- some we wanted to spend more time on but we did get to see many things. Activities on the boat were good for a river cruise. We didn't have any bored time, that's for sure.
We loved it and may try another river cruise sometime soon.
One negative was that we had a very difficult time finding a catholic mass.
There is more noise -- not really the soot problem mentioned by others at the back. If we do this again -- we will definitely go with one of the suites in the middle of the boat instead of the Explorer Suite at the back. But it was fun to be out on the back during the first few days when the deck was closed.