I had a very good stay at the Gallery Residence. It was my first time in Istanbul and I really appreciated the hotel's neighborhood, as I was walking distance from park, boutiques and restaurants. Plus, the staff of the hotel was very friendly and helpful.
The breakfast was ok for me, but this is mostly because I am lactose-intolerant so options were pretty limited. Indeed, it was generally very hard to get dairy-free options in Istanbul (as far as I saw), so this is not related to the hotel itself.
I found the room confortable and more quiet than other hotels I have been too in USA and Canada. A little detail though: once there, I found out that the tap water was not drinkable. Therefore, I did not used the kitchenette as much as I initially planned to do. I think it would worth mentioning this in the hotel description, at least for westerner travellers. Yet, I was very happy with this hotel.