Stayed there January 2001. Very nice property. Modern building with some elements of local traditional architecture (as usual in European/Asian Hyatts). Nice pool although it was too cold for it in January. Impeechable service, good food. Located in a little park (IC and I believe also Hilton nearby). Location is at the end of the western oriented shopping area with a little tram way running through the street. This very street also has a lot of nice restaurants. Only downside: To downtown with the bazar and the sights you need to talk a (short) walk to the tram way, take the tram, take an (equally funny) subway, walk across the Galata bridge and take the next tram and you will be there. Or you take a cab in the first place, which is rather inexpensive as already mentioned in previous posts.
Enjoy your stay