We just returned from Uniworld's 15 night Istanbul to Vienna with a Prague ad on. It was so totally different from an ocean cruise. The first 3 days were not what I expected, long bus rides to the towns and a day in the Iron Gates with not much to do on board.
The cabins are very small, not enough room to pass each other around the bed! Also, the French Balcony was wasted when we were tied up next to another river boat. We only had 80 people instead of 130 and I imagine it would feel crowded if the ship were full. Other than the 3 aforementioned ports, we docked in town and were able to walk to things. The included excursions were well done and generally we had plenty of time to be on our own. Days were busy with seeing the sights and we generally went back to our cabin right after dinner. We had 3 days in Istanbul with Uniworld at the start of the trip. The hotel was good as was the room, but the view was non existent. (Same with the hotel in Prague.) We flew as a group to Bucharest to start the cruise. It was nice to just follow directions and not worry about the details. This is the best way to see these cities as you are dragging your hotel and not your suitcase. The food was above average but not divine. Dinner was always on the gourmet side, very small portions. The staff was excellent. The entire experience is like a very mini ocean cruise. Nothing is over the top. Very comfortable but no WOWS from me. However, I would take another because I like being in a new port every day and I am running out of Mediterranean ports to visit! I also loved the complimentary washing machines, so convenient.