First, a caveat: I am not an aficionado of cruise ships, and furthermore the only two cruises I have previously taken were by Crystal Cruises and Oceania, so I not only may not know what serious cruisers like, I also probably have unrealistically high expectations for food, facilities and service. Having said all that, I did enjoy our cruise on the American Empress down the Snake and Colombia Rivers, and can generally recommend it, with a few cautions.
The short version: If you don't require polished 5 star service, perfectly consistent cuisine, always fascinating ports of call, youthful fellow passengers, and a deep roster of onboard entertainment, but do enjoy watching a variety of rugged scenery slip by your balcony, lazy days of reading and lounging, watching wildlife, day trips to view natural splendor, and learning the history of the land and the early explorers, this could be the trip for you.
The longer version, divided by topic: