The apartment is (almost) great.
For two couples, each with their own teenage daughter, we had enough space for all.
Location: walking distance to Sagrada Familia, awesome coffee place around the corner, grocery shopping near by.
Apartment configuration: a long corridor separates the 3 bedrooms from the living and dining rooms, which creates intimacy, if some want to play while others want to sleep.
Bathrooms were spacious. The kitchen had everything we needed. Overall was worth it.
However, there were some inconveniences:
1. No heating! If you visit during winter time, like we did, this might be a problem. It was very cold in the apartment. The balcony doors in one of the bedrooms are very old and so the wind blows strongly underneath as they don't isolate properly. After two nights of waking up with a terrible headache, I had to buy myself a hat and hoody to get some sleep.
2. Two of the bedrooms have no outside windows (natural light) as the windows open inside the staircase.