Felipe and Susana were wonderful hosts and very accomodating. We arrived earlier than their stated check-in time, and Susana left work early to meet us and show us their apartment! The location could hardly be better; it's located on the south side of the Douro, within easy walking distance of the port houses, if you don't mind the hilly nature of Porto. And, outside the apartment building door is the nearest Metro stop (Gen. Torres), so getting to the rest of Porto is simple, although reaching just about anywhere in the old quarter on foot is easy. Also, just around the corner from the building is the Gen. Torres train station which gives you access to the rest of Portugal, including the beautiful beaches at Espinho! (Although this convenience can be somewhat offset by train noise when windows are open e.g. if it is warm/hot in the apartment and you need to sleep with the windows open).
Felipe and Susana will give you some great tips on many other locations worth visiting. The apartment was true to the description and we enjoyed the space, the kitchen (and the dishwasher!), and the roomy two bed/two bathroom setup as we were four adults. Felipe and Susana quickly responded to a couple of minor issues that we encountered and resolved them without issue.
We very much enjoyed our stay!