Average Kadikoy hotel :) if you ever stayed in another one over there, you already know what to expect.
The owners were really nice and hospitable all the time, the location is far enough from the crowded streets, but close enough, if you want to go out. Also the ferry station is just in 5 min walk, as well as the bus terminal (make sure to use public transport in Istanbul, especially in the summer - it's really good!).
The downsides are typical for most places like this - you won't have much tableware if you're used to cook at home. There were just two tiny tea cups and plates for them and a teapot. But the fridge was also there, which is nice. Also there was some smell in the bathroom, plus if your neighbors will decide to smoke at their flat, your one will smell as if they were smoking in your bed.
The AC works fine and it's shady, so in the summer it doesn't get too hot. The bed is a bit worn and could've used a replacement, but is still pretty ok.
To sum up, if you plan a short stay and can stand some inconveniences in exchange for good location and hospitality, it's a good option