The apartment is located on one of Barcelona's main streets, very easy to find and to travel to/ from. With two small children we had to take taxis (very cheap, btw), but for adults, it's pretty much withing a walking distance from the main sights. There is also a metro station close by and the metro system is great (and cheap).
We really enjoyed the way the apartment is decorated. Although not really large, it's designed in a smart way to fit all your needs and has a spacious patio with a large parasol and beautiful plants. Another serious plus was the speed at which the hosts were ready to answer all our questions, even though at the moment of our stay, they were on vacation themselves.
The place has good WiFi and is relatively well equipped (TV, airco, very good linnen, pillows, towels, comfy furniture), although we did feel like the hosts should probably invest in more up-to-date stove/ washing machine. Also, the absence of a Nespresso machine was a disappointment to us personally, but there were an older generation coffee machine and a coffee brewer available. It should also be added that the Spanish are not particularly into tea drinking and it's difficult to find good tea in the local supermarkets, so bring your own tea. There was no teapot in the appartment either :)
The supermarket in the street two streets further is big but seems to be a discounter, we couldn't find any organic or gluten-free goods there, so maybe it makes sense to look for a Carrefour or another quality chain instead.
If you have small children and want to go to the beach, consider taking a 30 min drive to the beautiful beach town of Sitges instead of the local Barcelona city beaches. The latter have a great vibe as well but the former are much safer (in terms of waves/ depth).
We were pleasantly surprised at the ease with which one can drive into and out of the city and through the city, the traffic situation is very well though out. We parked the car several block away from the apartment, in an underground garage. That was probably the only expensive bit.
Also loved that we could just leave the keys on the table and leave on our last morning (without anyone coming to fetch the keys), this made the packing much less stressful.
All in all we've had a great time and hope to come back!