Our stay at the apartment was great. The location and view can't be beat, with easy access to the metro and taxis to get to the further sights. But honestly we just walked most places. There's a nice market around the corner and lots of nice cafes and bars for breakfast or a pre-dinner drink. We chose to go a bit further afield for dinner to avoid some of the more touristy restaurants around the Sagrada Familia.
Our one note is the apartment was a bit smaller than it seemed in the photos—it was a bit tight for the 5 of us, but that is probably more our fault than Mar's. We didn't spend much time there anyway since we were out and about so much.
All in all, a lovely 3 days in Barcelona!