We stayed with 2 adults and 2 children and it was comfortable for all of us. Good size for Tokyo apartment. There was enough space for me and my husband to enjoy glass of wine in the kitchen/living room area after kids go to sleep.
The room was very clean. No dirty spots behind the garbage cans or underneath the couch.
It was great to have a washer in the room since we traveled for a few weeks with kids and needed to wash our clothes. There is no dryer (most of the Japanese apartments do not have one) but the bathroom has clothes drying function. (You hang clothes in the bathroom and leave dry setting on for a few hours.)
I would love to stay here again when I come back to Tokyo!