I was only very short in Greg's apartment (stopover), but it's located perfect, 50 m from Gran Via in the center. But as well it is quiet because it's in the 6th floor in a smaller street.
The room was spacious and the bed comfortable.
All in all: perfect. When I visit Madrid again a very good place to stay.
The time I was there was too short to talk much with Greg, but he seems to be very pleasant.