We enjoyed our stay at Engin's place - very nice place, with nice furnishings! The apartment is quite close to Taksim Square & Metro therefore is easily accessible to the major landmarks in Istanbul. Engin himself was a very nice host and was very flexible with the checking in & out times, and even offered us options for transportation. The only disadvantage with the place is that it's on a steep hill up to Taksim Square (so it's quite a hassle with large luggages), but otherwise it's a great place :)
I recommend this place!