Small but liveable space. IMO the main selling point was how close the apartment was to various activities: despite being on a quiet-ish street, it's only a ~5 minute walk to innumerable shopping / drinking / dining experiences. Great as a jumping off point for experiencing Lisbon, but wouldn't recommend for any trip where you expect to spend a lot of time indoors (i.e. working).
Here's why:
1. Bathroom plumbing had an unfortunate smell and lacked a great system of ventilation, so this permeated the apartment whenever the door was open.
2. Apartment was overall somewhat chilly and damp. There were no heating options so whenever it rained outside (and even when we had clothes drying) the whole place felt a bit musty.