We did the Scenic 11 day cruise in July 2022 (with the Lisbon and Madrid extensions). It was different from our previous river cruises (Rhine and Danube), and I wasn't familiar with the language. I've got some fond memories now, though when we arrived back home I had the feeling that it was the weakest experience of our 3 river cruises - very good but not outstanding. But looking back at the photos and remembering the excursions, I'm glad I did it. Yes it was different from previous river cruises, and was paced more leisurely, but in hindsight it was worth it. It had a different "feel" to it that has taken me some time to fully appreciate.
As others have pointed out, at many of the docks there's not much close by to where you are docked, but on those days the evening's on-board entertainment was quite sufficient. In Porto and one or two other places you'll find on-shore options.
Most excursions were within an hour's bus ride of the dock. The ship's guides travelled with us and provided enjoyable commentary along the way, of history, geography, economics, culture, nature, etc. (The crew and staff were all from Portugal, which made for a more integrated experience than I found to be the case with the Rhine and Danube cruises.) Scenic uses their own buses, which are very clean and comfortable. There were one or two excursions every day except for a couple of "sailing days".
We took their excursion to Vila Real and it really was a slice of small town life up in the hills; very charming and rustic (I chose to buy my souvenirs there). One of the guides had grown up near there in an even smaller farming community - so for her Vila Real was a large town 🙂. Especially there at Vila Real I felt that rural Portugal had a bit of the feel of "eastern Europe" - a bit run down, but clean and safe, very proud of their history and culture.
We chose the bus tour to Salamanca despite regrets expressed by some on this board that it was a long bus ride, but I'm glad I went - I suppose it depends on how much you're interested in history and art; during our free time we visited the Art Deco / Art Nouveau museum which (lucky for us) was displaying all 100 of Dali's prints illustrating Dante's Divine Comedy; that was a major highlight of the trip for me. Salamanca was a long day, but we had several hours to wander after the guided portion so if you're in good shape and enjoy exploring an old, historic city, it's worth it. Or enjoying a coffee/beer in the Plaza Mayor, people-watching.
The Côa Valley Archeological Park is worth it if you're interested in paleology. It was really well put together, very clean and modern. The actual rock carvings themselves are difficult to get to (several hours in an ATV), so the museum mostly displays copies, moulds, and rubbings. They do a good job of showing how this site compares to other paleological sites in Europe and around the world.
We took their excursion to Aveira, south of Porto, for an example of a smaller seacost city. The guided portion was a canal cruise, in case you hadn't had enough water yet. 🙂 There was plenty of free time to browse shops afterwards.
So yes, it's a different sort of cruise from the Rhine or Danube, more leisurely and charming. It took me some time and reflection to appreciate it more fully. Of course it didn't help that we were distracted by COVID and the horrible air travel experience of 2022 and lost luggage - but now that those painful memories have receded, it really was a nice little cruise.