Berkan is a wonderful, thoughtful host. His place has an excellent location: right in Kadıköy; everything is easily within distance; clean; good amenities and lots of space. The main room is spacious and comfortable and has a good-sized balcony out back. What makes it special are the people. Berkan helped me out with a ton of stuff, including accommodating my 3 am arrival time, buying and setting up a desk for me to work at, walking me to the post office to mail something internationally (a hard task without Turkish!), and providing good advice on how to get around the city. He runs a tango studio, which means that you get an instant social circle of friendly and interesting people if you want! His two cats are probably the best animals in the entire city.
Overall, highly recommended for long or short stays!