Location! The apartment is in a great location. Principe Real feels like a neighborhood of both locals and tourists — less touristy than other areas of Lisbon we visited, which I liked. Great restaurants within walking distance (A Cevicheria, Loucos de Lisboa) and easy to walk or take public transportation to other parts of the city!
The apartment itself was clean and had linens and towels for all guests.
As of others have said, the narrow stairway to the third floor made bringing luggage up difficult, and the stairway light was out on the 3rd floor making it very dark at night. The light is something easily remedied.