Great quiet place for one or a couple. Not in the centre but easy metro/ bus access to the city centre. The neighbourhood is a vibrant multi cultural place which contrasts with the more fashionable areas of Madrid. I personally enjoy staying in a "real" neighbourhood.
Close to the flat is the Mercado Dona Carlota which is definitely worth checking out. Try a breakfast or a lunch in the great little cafeteria inside the market. You won't be disappointed and you will be pleasantly surprised at the prices!
Mariano is a welcoming and helpful host who keeps a great little place. Nicely decorated and with all you might need - I would certainly go back.