The stay was pleasant overall. Great location - some of the most popular sightseeing is just 15-20 min walk away (e.g., Prado Museum, Royal Palace of Madrid, Mercado de San Miguel, and others). Located on a shopping street but the noise from the streets can't be heard and doesn't disturb sleep or relaxation during the day.
The only cons: The walls are so thin that you can hear noises and conversations from the next rooms, but if you have a tight sleep as I do, it won't disturb you. It was a bit hard to communicate with the host because none of the staff spoke basic English, and all the communication was in Spanish. Luckily, somehow I figured out what I was told. And it was a bit cold during the night.
I'm sure I'd be more than happy to stay there during another trip to Madrid.