Angel is a very attentive host and tried hard to make our stay comfortable, offering a lot of advice. The apartment itself was spacious and comfortable.
But there were two things that detracted significantly from the experience.
The first is that the Gran Via subway station is closed until about March 2019 and there is no way to tell Google Maps that. Any subway route planning you get will incorrectly tell you to get off at Gran Via - the nearest on the same route is Sol. It's navigable with suitcases but about 400m extra walking. We recommend taking buses - there are easy connections on Gran Via.
The major problem for us was the night-time noise. This is partly a consequence of being in such a central location - for some people I'm sure this is a big benefit.
Even with the shutters down and the windows shut, the noise from the street was like being the other side of the wall from a big party going on until about 6am.
We were frequently woken by loud drunken arguments, or maybe just people enjoying themselves - we don't speak Spanish. Worse, there's an array of bins outside the apartment entrance. I'm a fan of recycling but people emptying dozens of bottle into a big bin at 2am is annoying.