Deniz' flat is located only a block or two from Taksim so it is pretty central to a lot of tourist destinations and the metro. There are several smaller groceries and markets less than a block away and everything else is either pretty close or a hop on the metro away.
As others have noted, the flat is a little atypical in the sense that it is actually Deniz' home and thus it is filled with his stuff but I guess that is what AirBNB is actually supposed to be. If you like pop art, the entire flat is ornamented with works from Deniz.
The flat is exactly as pictured although I would note that the bigger bed is actually a fold out sofa and you will more likely find yourself sleeping on the smaller bed which is really only suitable for a single person. Unlike other guests, I had no problems at all with the stove and the internet was more or less stable and fairly high-speed. The shower is exactly as pictured though I would note there is no fixture to hang the shower head from and thus it is hand-held while you shower, but generally accurately depicted in the photos.
Deniz himself was always quick in response to any inquiry I had and a minor issue I had was quickly addressed through a third-party as Deniz is or was out of the country.
All in all it was a great stay and good value for the money and location. I would stay there again if I found myself wanting central access to the Taksim area.