My boyfriend and I spent 5 nights at Koray's place for my birthday and had an absolute blast. Koray's apartment is perfectly located - it was our first visit to New York and we found it really easy to navigate our way to everywhere we wanted to go. Getting uptown for touristy things is a breeze, whilst right on your doorstep you have more bars, shops and restaurants than you could possibly ever visit! It's also easy to get to Brooklyn, which we were glad of as we really liked it there. A couple of stops on the subway and you're right in the thick of it - and being able to hop right back on at 4am to come home was amazing (as Londoners this was a bit of a novelty!)
As for the apartment - it's just like the pictures: bright, modern, spacious and clean. We loved the sound system with speakers in the bedroom and the cool (and clever) bathroom. The bed is VERY comfy which was great as we were always very tired each night after walking everywhere! We didn't actually meet Koray but the booking process was smooth, he was very responsive to any questions, and picking up the keys was a doddle.
As others have said the only drawback is the stairs (there are a lot of them!) but despite a heat wave whilst we were there we never found it a problem and trust me, the amount you'll probably eat whilst you're there you'll be glad of some form of exercise!
All in all we wouldn't hesitate to recommend staying at Koray's place and as soon as we can we'll be back!