All around excellent. Location is ideal for sightseeing -- entire city is within walking distance, but public transport options are abundant (directly on top of metro station, 5 min walk to suburban trains that serve Penedes, Sitges, etc, and 5 min walk to trains or express bus to Montserrat). Taxis were always within 2-3 mins away when called on an app, or plenty to hail on the street.
Apartment is directly on Passig de Gracia shopping district -- akin to staying on Fifth Ave in NYC or Oxford St in London. What comes with the location is that the loss of 'small neighborhood feel', but that's hard to come by these days in BCN tourist district anyway.
Overall great experience, and I would recommend for friends visiting BCN.