There are two metro lines very close to the apartment. Kreuzberg and Neukoelln are lively areas at walking distance. It is clean, warm in winter, comfortable. Maybe, if you expect to socialize much, the lack of common rooms does not favour it enormously. In my case it wasn't a problem at all. I was working in my room in complete privacy and with access to coffee and tea which saved the days.
The host was in contact by phone and mail, though I entered the apartment via a friend of his. Went smooth.