Great location - very central but still quiet. The apartment is very nice, clean and comfortable. We really enjoyed our breakfasts on the terrace :) There is also a public parking nearby which is very important if you travel by car as you cannot park on the streets.
Isik is a great host! We arrived really, really late (3 in the morning) but still he was there to meet us. He was very responsible and answered all the questions that we had. I would definitely recommend the place to all my friends who plan to visit Istanbul.