In one word: amazing. Very charming, clean, well-stocked and well-located apartment (not only a short walk from anywhere in downtown Porto, but also located right next to and across the street from great restaurants, coffee shops and bar).
Luis and Ines were amazing hosts, and very attentive. We received an incredibly warm "Portuguese" welcome. Luis' recommendations on what to do (and not to do) in Porto was spot on.
One word of advice: if you prefer a quiet place off the beaten path, then this might not be it. However, I definitely recommend this apartment precisely because of the authentic Portuguese experience (which is loud and constantly "alive"). It is located on a largo (a square) where you can sit at the window and watch (and listen to) the hustle and bustle of life in a Portuguese town (always accompanied by music).
If you are considering going to Porto (which you should), stay at this place if you can.