We had a great time at ichimaru's place. It was exactly as advertised: GREAT location, lots of room, and a wild basement.
6 of us were very comfortable. Though, there is only a curtain separating the rooms with the double beds. The proximity to Shin-Ōkubo Station and Seibu-Shinjuku Station made it a great launchpad for exploring Tokyo. At night we were surrounded by an overwhelming variety of restaurants and bars.
I wouldn't hesitate to stay here again!