Reading other reviews makes me wonder if people are talking about the same apartment that we stayed at.
The location, while it's decent since it's close to some of the main attractions in Istanbul, is in an extremely noisy and dirty neighborhood.
The apartment looks modern but it was quite dirty and lacked some basic amenities. The kitchen was infested with cockroaches which made it unusable and the host suggested that we buy our own dishwashing detergent.
The walls are extremely thin and you can hear everything that's going on around you (we had the misfortune of having very loud neighbors).
On top of that, in the middle of the night, somebody in the building was renovating because you could hear hammering and drilling.
Beware of poor internet/wifi speeds, as others have already mentioned. There were times when you could barely use it.
I simply cannot recommend this place.