We had a very great stay at Alex's house ! It is spacious, clean and we had everything we needed (would be even better if we could use gas to cook).
Alex is an amazing and friendly host who is available ! The metro station is literally in front of the flat and you'll reach the city center within 10mn. The Park Guell is very close as well. Just note it can be a bit noisy at night.
We highly recommend this place to discover beautiful Barcelona :)