Four of us (father, stepmother, daughter and son-in-law) stayed for a week in this terrific apartment. It is clean, sunny, very quiet, and well-located for food, La S. F., and the Metro. We agree with others' positive comments and to avoid duplication will add a few new ones:

*La S.F. is not just visible from the terrace, it's only a block away. Beautiful!
*One could easily take public transportation from the airport. The Metro is a block away and it connects with Estacio Barcelona Sants.
*The apartment is well designed for use of space. Note that the second floor is a loft with a big closet and bath. But it is a loft bedroom with privacy provided by walls and dark curtains. The downstairs bedrooms are at the front of the apt. and very quiet. The livingroom/kitchen/bathroom/loft areas are open and provide minimal privacy (if you're shy, run water when using the bathroom!).
* This is not specific to this flat, but if you are new to travel in Europe and are excited that the flat has a washer/dryer, note that loads must be small and drying is relative.
* The kitchen is nice and well-stocked. We only ate breakfast and snacks in, but could have easily cooked. There are two groceries on the block (closed Sundays though).
* Our only negative comment is that in the evening, the lights are quite dim. We're all readers and found that a challenge in the evening. But given the late evening dining hours, it wasn't a big deal.
* It's very easy to hail a cab right outside the door.
* Some have commented on a smell. Yes, the entrance hallway has a bit of an "old" smell, but it is not really unpleasant and it did not make its way to the flat.

We would definitely stay at this apartment again!