Just got back from Istanbul after staying at the DoubleTree. Great call. It is super close to Sultanahmet (area where the Blue Mosque is located) and near a tram station if you are wanting to explore more of the city.
The multi-lingual staff were top notch and getting to and from the airport can cost anywhere from 40-60TL (depending on traffic). 1TL= $.50 so Istanbul was super cheap.
Again a topnotch property that I would stay at again.