The location was fantastic, right outside the train station, a metro stop, and several bus stops. It was within easy walking distance of several museums (Prado, Reina Sofia), and the Buen Retiro Park. The apartment was clean, and sheets/blankets/towels were provided.
There was a washing machine and an oven in the apartment, as well as limited cookware and pantry staples (like salt and oil), which was nice. However, there was no microwave or dishwasher.
There are only heaters on one half of the apartment (bedrooms/living room side), so the kitchen and bathroom got very cold, especially at night. However, the bedroom was always cozy, so this wasn't a big issue for me.
The apartment is in an old building, so I would not recommend it for someone with mobility issues. The elevator was very small, and the stairs are uneven from years of use. The bathroom was very narrow and long, and it was difficult to get into/out of the shower as there was a swinging glass door instead of a curtain and a very narrow entrance.
Overall, I enjoyed my stay here, and would recommend it for its location, convenience, and cleanliness.