In short, great flat! I will write a list of pros and cons.
Pros: Close to Guell park, Next to supermarket, clean and modern.
There is a train and bus station which name is Vallcara. Metro L3, which will goes to center of the Barcelona. Also, Bus will goes to mercadona, which is one of the most famous supermarket in Barcelona.Easy to live in!
Cons: Dark especially morning(most important thing,you should turn on the alarm clock to prevent from staying up late), no answer when you left your baggage after you check out(I left my pan and I told to the owner, but no answer :/), hard to dry your clothes (but this is ok because the washing machine also contains dryer), littilebit cold when autumn and winter (there is a air-conditioner, but it's not enough to warm everything. You also turn on the heater, and it will be fine... for autumn), littilebit loud especially afternoon because most of the tourist will though this flat because it is next to Guell Park.