This was our second Viking river cruise following up on the Grand European. The smaller Astrild was much more intimate than the normal long ship. There were 95 passengers on our cruise, and it was very easy to get to know folks. The crew was outstanding in all areas. Our room attendant kept our cabin spotless and our favorite waiters went above and beyond to please. The food was delicious and plentiful. We had no water level issues so were able to dock at the normal Viking piers near city centers. The opportunity to tour the wheelhouse was very interesting. The river traffic was very light (only saw 2 other large vessels, one a vintage steam paddle wheel ship) unlike the Rhine and Danube and there are no locks. The scenery varied from the Saxon Switzerland rock formations to very flat farmlands.
If you like classical music, I'd highly recommend the optional "Concert at the Zwinger" at night in Dresden. It was a private concert (10 pieces) for about 14 Viking guests by five outstanding professional musicians from the Dresden Residence Orchestra in the ornate palace wall pavilion concert hall.
Berlin and Prague are interesting cities that need additional time on your own beyond the normal Viking package days to tour and see.
Our very comfortable French balcony worked perfectly for this cruise. We enjoyed having the ability to open the window occasionally. While the square footage is less than other cabins it is laid out very efficiently.