Outstanding. Lots of room, so everybody can choose to be together in the large common areas or have some "alone time" in a bedroom. Everything just works as it should—washer, showers, kitchen appliances—making for a very unstressed stay and the air conditioning had no trouble dealing with several days in a row of 38 celcius daily highs.
Location is fabulous. Around a 15 minute walk to the Prado, Reina Sofia, and Thyssen museums, the Retiro park, or Plaza Mayor. Nearest Metro station is 2 minutes away and there are dozens of restaurants in a 10 minute radius.