The Avalon Tranquility is a pretty ship with attractive if very small state rooms. Public spaces are very limited, except for the open top deck, which is unusable on some parts of the river (due to low bridges), and which becomes unusable in inclement weather.
The cruise director on the ship, Andre, was excellent - knowledgeable, friendly, and uniformly helpful. Ditto front desk staff. Cabin service rivals the best ships on the water. Wait staff, on the other hand, do their jobs just as they have been told, nothing more. If you are in for breakfast 45 minutes into the 2 hour time frame and there are no clean spaces, they are surly about setting up a clean space. At dinner, don't even think about asking for wine or water when they are "on program" doing something else. You will just have to wait.
Food on the ship is 2/3s wonderful. Breakfast and lunch are outstanding. Choices are many and at both, and the lunch menus vary by the day. It is hard to choose, but with buffets you can at least get small tastes of many enticing dishes. After such great beginnings, dinner is confusing. Choices are limited, servings are often small, and some of the dishes just aren't good. The first night in particular, many people (who had eaten light meals during bus transit to the ship) went away still hungry.
One positive aspect - the chef is willing to work with passengers with dietary requirements, which may limit the intake of spicy or high fat items. This personal service is a real plus, and can overcome some of the dinner issues.
Entertainment on the ship is limited but quite good. A lone individual played a variety of instruments and music, taking requests. The dance floor is small, but adequate for the number of guests. The only draw back is pre-dinner music is non-existent, as this is when port talks occur, in the lounge, which is the only place that accommodates all other than the dining room.
Daily ports of call were outstanding. There was always an included tour which either hit the high spots or at least gave some introduction to the locale. Optional tours were well run, although guides had a tendency to talk incessantly even after they had provided all the necessary information. The guides on the buses on the transit from Prague to Nuremburg "read" scripts very poorly, and seemed to be a holdover from the USSR days, praising local industries rather than providing local history and culture.
Because of the daily call at a port, and the limited entertainment, this feels more like a tour than a cruise. There are no sea days for R&R, and little time for just enjoying the ship and cruising.
However, it is a MUCH more pleasant and elegant way to tour than motor coach.