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.
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.