I enjoyed my stay at Kaya's apartment. It had everything I needed for my one month stay in Kadikoy and, in particular, I liked the big windows that let in a lot of light, making it good for long days of working from inside.
Also, Kaya is a very hospitable and patient host, helping me with advice and recommendations whenever I needed it.
Location is perfect for reaching multiple restaurants, bars and shops selling all kinds of local stuff that you probably wouldn't be able to find in most western countries.
Another positive: it's close to all types of public ways of transportation of Istanbul, from ferries to the amazing Marmaray.