Anyone gone on any European river cruises?

My wife and I are considering one for our tenth anniversary, going probably late June/early July. Any experiences you'd like to share? Cruise lines to recommend or avoid? Must-see cities?

We were originally going to do 2-3 weeks touring about, starting in London then going to Belgium and then running amuck, but starting a new job last November blew apart our plans. Now I definitely need a vacation and am planning on taking 2-3 weeks leave without pay to do it.

We're considering France, Germany/Czech, or Amsterdam down in to Germany.