Whilst I have only used accommodation from Airbnb etc. a few times, this was easily the best. The apartment was better than described, probably newly refurbished, well decorated, with a good kitchen and bathrooms. Communication with our host was timely and supportive.
(As a example of kindness the housekeeper stayed with us until our taxi arrived to take us to the airport. My Spanish is minimal and she would have phoned the taxi company on our behalf if the ordered taxi had not arrived as required.)
Firstly Barcelona is a great city for tourists. This particular area has a number of good restaurants and any number of cafes and shops including excellent bakeries. Think friendly Parisian restaurants and boulangeries and that about sums it up.
Secondly the apartment is close to a few must see architectural goodies and two useful underground lines.
Thirdly residents in the apartment block are friendly and courteous, though so was everyone in Barcelona.