As asked I am posting our opinion on the Elbe river trip we took from Prague to Hamburg in early August. We had been concerned about the 120 sq. ft. of cabin space but the improved design -especially the shower stall- was a pleasant surprise and there was plenty of room. The food was uniformly excellent on board and the crew both efficient and friendly. If we had had the time available we would have gone early to Prague. The short time there with the trip was not sufficient for this fine city.
We were not pleased with the side trip to Berlin -too much time on the bus and nowhere near enough in Berlin itself. We would have much preferred visiting Leipzig instead where Bach composed and performed many of his works.
The Elbe is not developed along the river bank much north of Dresden so do not expect the castles you see along the Rhein. However the small cities you visit near the river are interesting and provide an educational comparison with the non former DDR portion of Germany. Take good walking shoes as these cities generally have mostly cobblestone streets. The abundance of clean energy windmills and solar cells is impressive.
We were very lucky when we were in Hamburg in that there was a special art exhibition in town of the works of the English artist J. M. W. Turner a special favorite of mine. A hint for this and other trips is to always check on cultural events before or when you arrive in a city.