I'd read mixed reviews before booking, but for 3 nights it was a good price and you cant get a better location, so we booked.
I can only comment on our own experience, 31, 3rd Floor.
The lift does not stop at 3, but does stop at 2. If you have suitcases, take note!
The apartment was fine for us and our teenage daughter. It was clean, comfy and there was plenty of space when the sofa bed is put away. Basic kitchenette and small bathroom with a shower, but big enough, and clean. Good air con too, though fiddly to initially turn on with the remote.
Its a relatively modern apartment, and yes, some bits here and there are worn, but this didnt impact our stay and we would be happy to stay in that apartment again.
2 tube stations, Sol and Opera, within a 3 or 4 minute walk and many of Madrid's hilights are within a 20 to 30 minute stroll. Some are closer.