We enjoyed our stay at Gokhan's place.
The apartment is spacious, cozy and warm. It has nice location - 10 minutes walking to Sisli metro station, 5 minutes to Carrefour supermarket, 1 minute to fruits&vegs shop nearby. Wifi connection is stable and operates at a high speed. At this place you won't hear the mosque's call for the pray which is also an advantage for non-religious guests.
Gokhan is a great host. He helped us to lift the luggage up, was constantly available for any requests (purchased some kitchenware, helped with the heating), provided us with drinking water and even made gifts for our daughter!
I would recommend you staying with Gokhan! :)