After speaking with Deniz, I understand that I was the first renter for the apartment in nearly a year, so while I am giving three stars for my experience, I don't expect that this would reflect what everyone else will experience.
First, I had some issues checking into the apartment, as Deniz had to coordinate his housekeeper coming to drop off the keys. She was a bit late and we weren't able to communicate with each other (I didn't understand Turkish, and she didn't understand English).
Second, the WiFi wasn't working on the first night. I had to set up the router, but then Deniz needed to call the company to inquire about why the service had been turned off. This took about a day to be fixed. Deniz was kind enough to offer me a small discount for that day.
Lastly, the air conditioner wasn't completely working. This wasn't the end of the world, but it was something I had been counting on given the heat.
Otherwise, the apartment is in a great location in Cihangir. The amenities are solid (good bathroom, good kitchen) and there is an amazing (shared) balcony available.