This rental was adequate and serviceable, and our reaction to it was one of being underwhelmed. We would not choose to stay there again.
Strong points: excellent communication from Charles and Conrad, charming period details of building and some facets of the apartment, and the location, which was as we wanted it: in a low-key area close to public transportation but not too removed from the central part of town. Some of the artwork and decor was fun and unusual.
Weak points: the first impression upon entering is of a mildew odor from the bathroom that would unpredictably get stronger or weaker from day to day. (We stayed for 8 nights.) Two of the beds are not queens--they're twins pushed together, and are not comfortable, and the bedding is of middling quality. There were quite a few broken and lifted tiles thoughout the house, and I badly stubbed my toe on one in the bedroom. The kitchen cookware needs a refresh, especially the dangerously dull prep knives. The kitchen also has only the bare minimum needed to cook, which surprised us, as most Airbnbs that we've used typically are stocked with the oils, spices, etc. of the previous guests, and this one was not, which means you will have to everything aside from salt and pepper. And stone floors everywhere might be nice during summer but were freezing in winter--a rug or two would be welcome. These are the kinds of things that we rave about with 5-star hosts, usually ones that host us in their homes, and it could be that this is typical of investment rentals.
Also, the area can get noisy, being that the apartment is on the main Boulevard, Gran Via. At night with the windows closed in winter it wasn't too much of a problem, but in summer I bet it could be.
Overall, we expected more for the price paid, but this wasn't awful, and we would just caution future guests not to be taken by the thrill of a period Barcelona apartment, and understand what they are getting when they sign up.