We thoroughly enjoyed our stay at Greg's place and will happily recommend it to our friends. Greg is a likeable guy. It's true that you can occasionally hear his footsteps above, but we did not consider this an issue. The neighborhood is very quiet.
Don't be deterred by the souterrain location - the place is bright and friendly, and tastefully decoracted. It's more spacious than the AirBnB post suggests - the profile is not doing it justice.
The one improvement we suggest is to equip at least one or two windows with an insect screen to allow in fresh air while keeping insects and squirrels out.