I stayed here in October 2014 as a Gold on points
Was upgraded to concierge level corner room -- appx 400 square feet. Very large bathtub and view on the 28th floor (I think)
Concierge lounge was excellent, and well-provisioned like an east Asian lounge. Amazing views of the city.
Downside at the time was that many of the cab drivers didnt know where it was, and the public transit access wasnt very obvious, although by day 2 I figured it out.
The hotel is NOT near the main tourist sites, but the Istanbul metro system is extensive and cheap. Figure 30mins to get to the main tourist locations on public transit.
Hope this helps!