Indirect knowledge: my wife and her mother did a river cruise
(the Seine, Paris to Normandy) a couple of years ago and loved it. Small boat (maybe 150 - 200 passengers) so you don't feel like you're in a crowd and the service
is more personal. Most of the travel was by day, so there's plenty of scenery, and it included stops in interesting places. I don't recall
them mentioning "excursions" in the sense of what you get on large cruise boats - just the chance to visit some of the towns you pass through.
Only possible negative I can see - I have visited that area at that time of year and you want to bring warm clothing
. On the other hand - assuming you're there before Christmas
- you'll get the Christmas
markets, beautiful scenery with a different look than what summer visitors see, lots of mulled wine.
Okay, that's it, you've convinced me. I want to go back to Alsace!