And DW loves to unpack just once on a trip...
Absolutely the biggest single advantage of a river cruise, and not to be dismissed lightly.
We have also been charmed by two or three places we saw on river cruises and gone back there on our own later. Train travel in Europe is so easy that there's no reason not to. In fact, my number one criterion for picking a hotel there in any city is that I want it within walking distance of the central train station.