Purrrfect location - Las Ramblas is a 3 mins walk, the Boqueria food market is 5 mins (you *must* go there!), non-stop supermarket is 5 meters away, there's a pharmacy in 10 meters, lots of great restaurants, Starbucks at the corner, etc. It's probably at the very best location in Barcelona.
The apartment is perfectly clean, with stunning views from both balconies (the cathedral, Sagrada Familia and more), and has everything you need - air conditioning in all rooms, a big fridge, everything for cooking, a dishwasher, and a washing machine with a dryer (make sure you have Google Translate handy for it though :).
The staff was super friendly and helpful and were replying to my Airbnb messages almost instantly. We were allowed to drop our luggage at Unique's offices on the last day and make the most out of it. The staff then called us a taxi (with an English-speaking driver - a big thing :) to the airport.
NB: the elevator broke on the 4th day (out of 7) and the apartment is on the 8th floor with a *super* steep staircase.
All in all, I'm rating it 4.9 of 5 (-0.1 because of the elevator).