A very nice studio apartment which has everything you'll need (including a washing machine and an iron). I also appreciated that in a snowy march the apartment was very warm and had a very good location (5 minutes from a tram and 8 from a metro station).
as for the negatives, the are almost none - i would mention only that you could hear quite a lot of street noise (which did not particularly disturb me) and I would also appreciate bigger glasses in the kitchen, but that's really an unimportant detail.
Overall a perfect place to stay in Istanbul.