We did the 7 day river cruise with 2 days on the Front end in Paris then Trier to Nuremberg and 4 days on the back end in Prague. Viking was outstanding and had staff in place to support us from our arrival at the airport in Paris until our departure at the airport in Prague. You will not be bored. The bus tour in Paris was great.
You have time on your own to do what you want as well but make sure you try to book those well in advance (months) so you do not have to stand in lines. On board the food was great and we loved the staff from the captain on down to the housekeeping staff.
The boat is small enough that you get to know the staff and they are so friendly and helpful and they CARE. The captain and director are their to meet everyone as they come back from the shore excursions. The castles, churches and local guides were knowledgeable and entertaining. The head sets were very helpful. Wish I could have recorded everything that was said to match up with the pictures we took.