Very nice staff, quiet property - something rare in Istanbul - good working air conditioner, comfortable bed, lots of storage, great shower, private balcony attached to room, elevator, and walking distance to grocery and 20 minutes downhill to the Besiktas city centre. Free daily breakfast included.
On the other hand, Wi-Fi is very slow, housekeeping is very hit or miss, and despite listing washer and dryer as an amenity, it's not accessible by guest and an extra fee to have clothes laundered by staff.
Overall, a very good, comfortable stay with a few shortcomings.