Great location right down the street from Plaza Catalunya. Metro and bus are very close by, giving you easy access to the entire city. Taxis are also very accessible via the taxi stop right across the street. The 24-hour supermarket next door is also very convenient for picking up snacks, water, and whatever everyday items you might need on your trip.
Host is kind and quick to respond; the man who was responsible for checking us in was kind and helpful as well.
Unfortunately when we arrived, there were several cleanliness issues. The shower curtain had started developing mold and should be replaced. A few of the kitchen items (like coffee makers) are old and appear stained/dirty, could use a deep cleaning. Both the bathroom and kitchen sinks were clogged and would quickly fill with water, taking a while to drain; upon informing the host he quickly scheduled a plumber, though we would have arrived after we checked out.
The elevator had been out of service for six days when we arrived. Obviously the elevator is out of control of the host, though I wish I had been informed beforehand.
Noisewise it is as you would expect as an older building on a relatively busy street. The apartment is up on the fifth floor so noise from the street is minimized. Sound does travel through the hall and walls, so you may hear others depending. Something for light sleepers to note, but no issues for sound sleepers.
Overall an ideal location for any traveler, and assuming the issues I described are fixed, a good place to stay.