This apartment and our stay were beyond excellent. We are a family of four, with two young kids, we stayed for a month. The location combines all the best things in Barcelona. It is in Eixample, Barcelona's signature neighborhood with octagonal city blocks. It is also 3-5 minutes walking distance from El Born, an older neighborhood with more narrow and twisted streets. Bars and restaurants are in abundance, just do your googling and you are all set. Transportation options are also great: subway and buses work nicely, it is a 10-minute bus ride to the seaside.
The apartment itself is very spacious. Hardwood floors, super-comfortable beds, all the amenities a family needs.
There is a smaller (but still the size of 2 city blocks) part 5 minutes from the apartment. There is a huge Ciutadella park nearby. If you stay with kids for a long time, get a yearly pass to the zoo (in Ciutadella park), it is cheaper than two visits for a family of four.
Finally, I can't thank Laura the host enough. She was very kind to us and supported us well beyond any expectations.