I am currently staying at the Istanbul Edition and leaving today, 5 days early, due to their poor service at this hotel. I have found their entire front office staff to not only be unfriendly but also incompetent and an utter lack of help. I will post more in depth on my experience here once I am home and no longer on vacation, as I do not wish to waste any additional vacation time. I have contacted the Platinum customer care folks and am transferring to the local Ritz Carlton, where I am optimistic that they are aware of how to provide some modicum of service unlike the Istanbul Edition. If the Istanbul Edition is any indication of what The Edition line of properties is about, I suggest sedition!
I have no experience with the IE, but stayed at the Renaissance Polat, which was absolutely wonderful. It's not in the center of Istanbul, but is easy for tours, and is right on the sea with a beach. I loved the place. The Concierge Lounge was closed because I was there during a holiday week, but they more than made up for it.
I hope the hotel doesn't ruin your trip to Istanbul -- I found it to be an amazing city and even took a flight to Ephesus one day that the Polat arranged as a tour.
planning on a visit to Istanbul and found a new Marriott in the business district which seems very nice---Platinum Elite and don't want to spend 384 euros or 200000 pts for stay at Ritz---stayed on a previous visit and was not overly impressed---thought service was far better at the Swiss Hotel that I used in early 2000s---would love info about new Marriott