Overall, a good place to stay, although extremely expensive. We stayed a month and paid $9,000 USD!
Cristina and Josep were very attentive and answered any questions fairly quickly and they really wanted to make sure our stay was a good one. The flat was very centrally located with access to just about anything and it was on a high enough floor so the noise from the street wasn't too bad. The beds were comfy and the air conditioning worked extremely well in the heat of the day. One bonus was that the elevator in the building was extra wide, which is rare for Barcelona!
The kitchen was missing some very basic items that we had to go out and purchase...not a big deal, but if we're spending that much money, we would think it should be well stocked with everything we needed. The owners offered to reimburse us for the items, but we ended up just gifting them to the house.