Communication was excellent. Cristina replied promptly to any questions we had. She and her son were waiting for us when we arrived to show us around the apartment and talk us through the map of the city and metro system.
The apartment was lovely and very clean. We were out nearly all the time and only slept there but the beds were very comfortable and there was plenty of equipment had we wanted to eat in or do some washing etc.
We loved the area - it was close enough to walk to the metro stations or anywhere in the city but away from the really touristy areas, which was a bonus for us. There are lots of restaurants nearby and we particularly liked sitting outside in the evenings at the bars in Plaça de la Virreina and Plaça del Sol.
The best restaurants we ate in were Tapas 24 (wonderful food), La Bicicleta (near the apartment and we ate there twice) and La Vinteria dell Call. Escriba does amazing cakes and breakfasts. We went to the patisserie but there is also a branch in the Rambla.
OneOcean Club is a great bar with lovely views of the marina in Barceloneta and there is a brilliant rooftop bar (1881) for cocktails as the sun sets on top of the Museum of History of Catalonia.
The Gaudi was amazing - Sagradia Familia (in the afternoon sun), Casa Battlo, La Pedrera, Park Guell. We found we could book tickets online just before we visited to avoid any queuing.
The only downside to the trip was discovering a passport had gone missing as we were due to fly back. We presume it was stolen at the airport - and met others who had a similar experience. The British Consulate were great at sorting an emergency passport in under 2 hours once they were open on Monday but it meant we had to stay another night in Barcelona. Cristina was really helpful and met us back at the apartment so we could stay another night which was a big relief - but be warned and keep a tight hold on your valuables at all times, particularly in the touristy areas!