The actual cruise is not like the other river cruises we took on the Rhine and Danube as except for Porto the places where we docked were of no interest, just small towns along the Douro. The actual trip starts with 2 nights in Lisbon, if I were going I would take extra days as you really only get one day and it is taken up in the morning with an included tour so if you want to see Lisbon go early, we did 3 extra nights as we went out to Sintra which is a must and the coast.
The day from Lisbon to Porto is an all day bus ride (which they should tell passengers how much time will be spent on the bus, as sites were not near the river). We stop in Coimbra for lunch with Fado show and a tour of the university but it's a whole day in the bus arriving at Porto and the boat before dinner so no time to go anywhere on your own. We received an email the day before our tour started that they were having issues on the river and we may not sail as the 2 weeks before us ships either did not sail or got stuck on the river as water was too high or could not get clear to go through the locks(we heard that Viking gave the next cruise the option to cancel because of the river issues).
We had 12 days of sunshine which may have helped our ship as we got through 3 of the 6 locks. There is a lot of bus riding to get places which Viking really should state in their package. The ships on the Douro can only sail during the day so, you are on the bus getting to places of interest and the ship is sailing to the next docking place where after a day of touring on the bus you meet the ship. The day we went to the Mateus Palace it was an hour and a half each way and only one hour at the Palace and Gardens so we didn't see much. Our tour did a whole day of sailing to get as far as we could on the river then everything was buses.