After doing 20 ocean cruises, we just returned from our first river cruise on Uniworld River Empress and absolutely loved it!
The itinerary (Basel-Amsterdam) was fantastic, with mix of some larger cities (Basel/Amsterdam overnight, Frankfurt and Cologne) and some smaller charming villages/towns. Highly recommended.
Uniworld is one of the most inclusive lines, and it's considered a luxury river line. We had two shore excursions that were extra (and very reasonably priced), everything else was included - gratuities, one excursion in each port (typically choice of 2-3), wines and spirits, Internet and shuttles to town.
Cabin tiny, but manageable. For people with mobility issues, could be a problem.