First of all I have to say that staying at Javier's place had been a positive experience for us. Didn't have a single issue.
The apartment's location is perfect. It is literally a few steps from La Sagrada Familia, walking distance from a metro station and surrounded with cafe's, restaurants and markets. The place is adequate for a family or a group of four. Not as a minus but as a reminder, the apartment is located in a central location in a city that lives 24 hours, next to a world famous touristic attraction. So as one can expect there is some street noise. I personally loved the location and didn't care about the noise.
The only thing that was less than expected is the shower. It was the smallest I have ever seen. So if you are large you better take this into account.