Aside from 3 points, the rooms are very good: 1. The door to the shower did not have a good seal with the floor, so water would get everywhere. 2. No soap dispenser in the bathroom. 3. The AC is good until you close your curtain, then it gets pretty hot.
But aside from this, the rooms were quite comfortable and there was a significant amount of privacy in my bunk once I closed the curtain (though it was pretty hot).
The service was excellent, staff always ready to help you in whatever way you needed (special mention to Miguel, who was amazing).
I didn't use the terrace or kitchen, but I did look at them and checked them out, and they were pretty nice.
It isn't physically next to or within 10 min walking of anything special, but the Navas station of the L1 métro is right down the street (take this one, not La Sagrera, even if you're going in the direction of La Sagrera). The Sagrada Familia is only a few minutes away by metro. The area itself is very nice and safe. There are some shops across the street that stay open until 5am, just look for the places that have lights on.
Honestly, unless you're across the street from a famous landmark, nothing matters except metro access, which this place has. (Tip: buy an Hola Barcelona card).
Overall, 4/5. Would be a 4.5/5 (a 5/5 as far as hostels go) if they iron out the kinks like shower sealing and bathroom soap.