Before I write anything, I should mention that the host is a very polite and professional person who is always responsive to Airbnb messages.
About the apartment, the location is quite lovely, and it's 30 steps away from Istiklal street (one of the main touristic areas of Istanbul). But being close to that area does not necessarily mean you'll enjoy it more because everything is more expensive in that neighborhood because of so many foreign tourists. So I would be mindful next time to get a place outside the main touristic areas.
The road the apartment is located in has a few bars, and the apartment is not well soundproof. Therefore you can hear constant music and loud speaking/shouting until 3 or 4 in the morning.
Those bars' noise can be problematic if you're sensitive to sound noises at night or have children with you. However, if you're young people whose night music does not bother you, this is a place for you.
The room with the yellow wall had a water heating system, and it was turning on and off during the night, and you could hear the firing sound of it. In the same room, you could hear the elevator going up and down (probably some of the elevator's equipment was on that room's roof). Those noises made me wake up a few times during the night.
The furniture was not of good quality, especially the dishwasher which was not cleaning the dishes very well. Also, the refrigerator door was kept open, and you needed to push hard to close it; the toilet flush would take around 10 minutes to get full of water, and it couldn't flush anything during that time ¯\_(ツ)_/¯
The staff was very nice and friendly, and they could quickly respond and come and fix things, and we had no issue with them.
The apartment was clean when we got it, and they have someone who comes after the checkout to clean up the apartment.