First time staying at an AC. They cut corners on a few things, but also provide most of what you need.

Central location and walking distance to many places. Five min to Atocha station, 5 minutes to Reina Sofia, 15 min walk to Prado.

Rate was $200/night, a bit steep but then again it is central Madrid. Breakfast is overpriced (26 euro), though with two guests Bonvoy Plats and up can get 18 euros in credit per day.

I was getting double elite nights and bonus points, but in the future I would probably stay elsewhere given the high cost for room and breakfast.

Positives
Quick check-in, upgraded to junior suite with twin beds. Room was pretty spacious, maybe 35-40sqm. Couch, coffee table, round desk/dining table.
Robes
Waterjet bath (powerful and blasts water out of tub if you aren't careful).
2 TVs
Lots of USB/electric outlets
Fairly quiet (end of hall)

Minus points
Paper cups for tea and coffee
No box of tissues, just tiny packet
No view
No hand lotion/moisturizer
Hangers in closet are anti-theft and can't be used anywhere else (we didn't want to hang wet jackets in closet)
Key card stopped working second day at noon, well before my confirmed late-checkout time