Barcelona was a pleasant surprise for me. The appeal of the city was in the everyday things, more than it was in the usual tourist attractions.
That said, Marta and Paul's place was PERFECT for taking in the Barcelona vibe. The usual compliments would be: the nearness to Sagrada Familia, to stores, to trains, to markets and cafes, the charm of their house, and the relaxing feel when you do stay in. My personal favorite is how i can instantly connect to the city by opening the window and the terrace door.
Tips: try the tapas bar that is 2 or 3 doors to the right (if you are facing the building entrance from the street). Gin & tonic, pulpo, and gambas. It wont look like it from first glance, but they have some of the best food and the most charming servers.
Also, every cafe within 2 blocks of the building has excellent coffee and bread. The rambla area and barrio gotico, not so much.