looking for input on Douro River Cruise

Have you looked on the Cruise Critic website? They have a forum for River Cruises. https://boards.cruisecritic.com/forum/115-river-cruising/

We’ve done the Viking Cruise. It is definitely a chance to slow down and relax. The land portion is too short (we spent several days in Portugal before joining the tour), but you’ll solve that with the 12 day tour. Once on the boat, it’s pretty lazy. There is one excursion per day and they are pretty low stress. There is usually a half day of cruising (except on the Salamanca day). The views are beautiful from the river and also while driving from the valley into the mountains for the excursions. The Douro scenery is best further up the river, so the scenic cruising is significantly better than what you can get on a day cruise from Porto.

It’s a bit of a booze cruise - every excursion included a drink (or more) and we were often welcomed back to the boat with a cocktail. Overall, it was very pleasant, low stress touring. I did a lot of knitting sitting on the top deck watching the scenery go by. I wouldn’t recommend the tour as an only visit to Portugal, but if you have time it pairs well with other touring or as part of a return visit to Portugal.

We did a day trip up the river and the scenery became monotonous, all terraced vineyards. Is this cruise scenery similar?

If your main goal is relaxation they the river cruise might be fine. The Douro is one we haven't done yet. We have done the Rhine, Rhone, Moselle, Danube, and Seine with Tauck who also have added the Douro. Love river cruising and it's nice that you can chose to go on the daily excursions or not and you can unpack and not keep moving hotels. Our favorites have been the cruises where we were docked right in the tourist locations so we could just wander from the ship to the sights at our own pace (Danube and Rhone were best for that). I will warn that river cruise ships do not have nearly the on board activities that big cruise ships do.

I didn't find the scenery monotonous, but I imagine one could. I thought the scenery was much better further up the river than one could reasonably travel on a day cruise.

Onboard activities were definitely limited. They expect you to eat, drink and look at the scenery. We had previously taken another river cruise with Viking (with the same companions, who have taken something on the order of 15 Viking river cruises). The big difference on the Douro cruise is that the tourist excursions were all a bus ride away. The river is down the valley and many of the sites are up in the hills. We were expecting that, so it was fine, but you don't have the same options to step off the boat and do things as you do on other river cruises. That said, we ate some meals off the boat in the small towns where we docked and loved that experience. I think our party was the only one on the boat to do that.

Thank you for the several helpful responses! We have booked the cruise and are looking forward to it, eyes wide open.