Can't recommend this apartment highly enough. It's right on the main plaza of Villa de Gracia, a human-scale neighborhood with plenty of markets, shops, bars, restaurants, and street life. Peaceful at night and lively during the day, it's just a short walk to the best known sights (Sagrada Familia, buildings and parks by Dali and Gaudi, etc.) and a few blocks to bus lines and the metro to visit the rest of the city.
The apartment was spacious and spotless, down to the individual pieces of cutlery in the kitchen. The beds, sofas, and other furniture were very comfortable; towels and sheets were super clean and plentiful; and the building itself is well maintained. The balcony offers the best view of the all the goings-on in the plaza, which during Carnival month were plentiful.
We stayed for a full month. Host Javier did an excellent job of staying in touch, arranged for periodic housekeeping for us, and made sure everything was in order.