I'll start with positives (because you may find the positives enough to overlook the negatives). It is a large apartment in a residential area (which we like). The view from the upstairs bedroom balcony was great. I will say the walk-only street leading to the place was very dirty (filled with trash)...nothing the owners can do about that.
The house/apartment was old (which is fine), but in real need of updating and basic repairs. I'm sure it was clean, but did not "feel" clean. If you're traveling in cooler months, it's probably fine, but if traveling to Lisbon in warmer temps, the place is hot...and we were instructed that if you leave the windows open that neighborhood cats might come in....we still left windows open at night. They did have fans that helped a lot...and the evenings did cool down a lot.
Overall...it was an OK place to sleep...but I personally would not stay here again or recommend it.