The apartment had a beautiful location, very near everything. Even attractions like the Santiago Bernabeu stadium are 10-15 minutes away by metro. Also, the large walls of the place ensure that the apartment is not getting incredibly warm during the summer.
We were with five adults, which seems to be the right amount except if you have children.
Also, our hosts were very good. They responded very quickly and were very warm. When we had a send a small request in the evening, they responded immediately and acted on it the next morning.