The apartment's location is its key asset. It's right next to Casa Mila and Casa Batllo as well as Barcelona's extensive Metro system, which lets you visit other of Gaudi's creations and other sights.
The apartment would have been perfect for a couple but with three people it gets slightly crowded. Otherwise, the furniture and other equipment are kept in a good condition. The slight downside is that we could not get the kettle to work and there was no tray or rack for the oven, so we could not really use either.
The outer walls of the apartment are rather thin, so you can hear your neighbours often, especially at night. The street is moderately loud during the evening because of nearby restaurants and other venues. On the upside, the street seemed to be only reserved for pedestrian/cyclist traffic with a few motorbikes/scooters every now and then.
Please, beware that if you arrive in the evening, there is a late arrival fee starting at 20€.
The host was nice and very quick with their replies.