Pros:
Location is great, right down the street from the train station.
Plenty of places to eat and drink close by.
A super market was right down the street.
Internet was fast.
The apartment was super clean.
Host was very responsive.
I would easily stay here again next time I'm in Madrid, and I'm in Madrid often.
Cons:
no self-check in (not a big deal...still 5 stars)
Took some time to heat up the place when it got cold.