This apartment has an amazing location, and you won't sound noise from the street (even that the neighborhood is very lively).
It has perfect size for one (and I think that even for two), as it's the same size as an average European hotel room. It's clean and contains all necessary amnesties (for the kitchen, the bedroom, the bathroom etc...).
Like written in previous comments, it only has one window in the living room, so there isn't a lot of daylight. It doesn't bothered me at all (and you if you are planning to go out and see Madrid).
And the most important thing are the kindness and the amazing hospitality of Emi - with "insider" recommendations and a fun fruits bowl.
Will definitely stay there again!