The place is located in lively neighborhood of Sol, a stone's throw from Puerta del Sol. Nearby streets are filled with restaurants and tavernas. Noise from the streets below can be heard inside the apartment. I didn't really mind about this but if you have sleeping challenges this should kept in mind.
The apartment itself is compact one, with two small rooms, miniscule kitchen and spacious bathroom with bath tub. It fits two people nicely. With three people the apartment may get cramped up.
If you are planning to do lots of cooking yourself you may prefer having a larger kitchen. On the other hand if you want to familiarize yourself with Madrid's lively restaurants (as you should) the kitchen is more than adequate for occasional simple cooking.
I spent the last week of March here. The couple first days were quite chilly which made the apartment a tad too cold for my taste although there was a central heating. This may be a more of a cultural thing as in Finland the apartments are kept quite warm around the year regardless of the weather.
Overall my vacation was very good. The location of Ana's place was awesome. During our stay we used underground only once as everything was within a walking distance. If you are staying in Madrid be sure to taste Jamon and wines of Ribera del Duero!