Great stay in Barcelona. The flat was nicely designed, though showing some signs of wear, especially in the bathroom. But still very modern and very clean and minimalistic while still feeling homey.
The flat was well located within a mile of the Sagrada Familia and right across the street from Hospital Sant Pau, which you have a beautiful view of from the bedroom balcony. There are lots of restaurants, coffee shops and stores in the area, and several bus stops and metro stations. We were met at the apartment by the manager, and she was great about marking popular spots on a map and offering suggestions for places to check out, as well as places to avoid. That overview was incredibly helpful.
We took the metro and buses quite a bit and the flat was well located for that. In about 15 mins on the metro, you can be on Passeig de Gracia, and from there have access to areas like the Gothic Quarter and El Born.
Being located at the intersection of larger roads, there is traffic noise and from the pedestrian plaza next door pretty much all night. I sleep with ear plugs so it wasn't much of a bother but it may be for some. Also, there is sometimes an odor of sewage that comes through. This is a problem in certain parts of Barcelona in general and doesn't have anything to do with the building in which the flat is in or the flat itself, but the area is affected by that odor sometimes, which comes and goes. The elevator/lift was also perfect to have if you're carrying heavy luggage. Lots of the older buildings don't have them but this one does, which is a huge plus.
Overall a great stay and would definitely stay again.