We had a very nice stay in Marcello's apartment. He is an excellent host who responds within minutes of a query or message (gracias, Marcello!). We also appreciated the early check-in, which was great.
Other pluses: excellent air conditioning, excellent wifi; comfortable bedrooms, with dedicated air conditioning; an elevator in the building, for schlepping baggage (guests must climb short sets of stairs to access elevator and apartment, but the travel between floors helps a lot); washing machine (drying rack for clothes is under the sofa); dishwasher; very convenient to grocery (a block away, and not a block with a steep hill, either! :) ); convenient to the metro (L3 line, Vallarca station). I love the Park Güell, and it's a short, steep climb to the entrance. The surrounding neighborhood is very hilly and primarily residential, and about 20 minutes away by the L3 metro from the Ramblas and the Barceloneta. Only a short walk to the fun spots in Gracia.
Guests might want to bear in mind that the bedrooms are the high point. The living room/kitchen area is very cute and nicely decorated, but it's quite small. We had a nice time, but that's because we are a family who really gets along well. We were definitely on top of each other. The bathroom is a little worse for wear, but it is clean.
As is fairly common in Spain, minimal dish soap, laundry soap, toilet paper are provided. Be prepared to pick some up at the store.