The apartment is the nicest place I stayed in Istanbul. The Kitchen has modern appliances that work fine. The bed, chairs, and sofa are all comfortable. The WiFi works great. It is about as quiet as you can expect in central Istanbul. The location is on a non-busy one-way street, and you can easily walk to Taksim Square and a bunch of restaurants, grocery stores, shops, etc.
However, you still can hear noises from the street as motorcycles drive by and people yell at each other. And you can hear your neighbors every time they watch TV or turn up their music. So bring ear plugs. Also, the bedroom isn't completely dark, so you may need a sleep mask at night. The A/C doesn't have a remote, but the temperature wasn't hot when I visited. And the hot water in the shower and kitchen taps is finicky; the temperature goes up and down and doesn't hold steady.
The host is great at communicating and accommodating guests. Cem let me know as soon as the apartment was ready to check-in, and he met me at the entrance to help with luggage. He was very quick to answer questions, and I appreciate his help.