Location! Location! Location! Super central, with access to all things in the center of Madrid.
Would recommend for a short-term stay.
However, stayed there a month, and I would not recommend for a long-term stay. The building is predominately (if not all) rentals, and there are inconsistencies in the ways other guests follow rules or are considerate of other guests. Late night parties, smoking, loud music, etc. While the apartment does have a functional kitchen, it's rather small and mainly for storing/reheating food. However, that's less of a problem given that the location is so central and there are tons of great places nearby for food. The water heater was inconsistent. It was often the case that 2 people could not take a 2-3 minute shower without running out of water. Also, the only windows are onto the interior of the building, so there's limited natural light, but you wouldn't notice if you spend all day outside the apartment. Wifi worked great.