Marta's place was excellent - the decor was lovely with lots of space and very comfortable. There was some street noise the first night and noise from the flat above the last night but very quiet otherwise, none of this really bothered us. The place was warm enough with the heating and I imagine nice and cool in the summer. The facilities all worked fine and we had no problem finding the place.
The location was great - very easy to access the city and the metro. There are lots of restaurants in the local area, the supermarket is a short walk away and the Plaza de la Paja is beautiful to sit in - Highlights were Cafe Delic & Dr Limon which were good value, the street market at El Rastro was fun and the river was good for running.
Marta was very responsive and helpful, we didn't meet her but the cleaner let us in and was as helpful as she could be.
Great place to stay in Madrid!