Andres is a fantastic host and the apartment is wonderful. Extremely comfortable, incredibly well equipped (more kitchen equipment than we have at home!!), spotless and in a great location. We took photos of the apartment, especially the kitchen; Andres has an exquisite design sense and we plan to copy a couple of the things he has done with the apartment. The balcony is great and you do indeed have amazing views, with the wild Gaudi church at one end of the street.

As for the location, just enter the address on Google Maps and then marvel at how close the apartment is to everything you might need or want: grocery stores, bakeries, bars, restaurants, coffee shops, the subway system, etc. We ate every night at excellent restaurants within easy walking distance of the apartment. It is also possible to walk to nearly all sites (if you are a fan of walking), but the subway system is well organized and the Sagrada Familia stop is a few minutes down the street from the apartment. We used it a lot. Avinguda de Gaudi itself is a wide pedestrian zone with benches and trees and outdoor seating for the restaurants and coffee shops that line the street. By the way, Andres' wi-fi is killer; I was able to use it to access the internet while seated on a park bench out on the street.
Andres sent us lots of useful information before we arrived and was at the apartment to meet us--with a bottle of Cava and a selection of chocolates. He had also provided coffee (for the Nespresso machine), milk, juice, mineral water, cereal, tea, and sugar.
Andres checked in with us a couple of times during our stay to make sure all was well. We only needed to contact him one time with a question and a call to his mobile phone was answered immediately.
If you plan to visit Barcelona--and you should, for it is a remarkable place--we enthusiastically recommend Andres and his apartment.