Sea Tower was fantastic, and the view from the balconies and sitting area is as good as advertised. The place was clean and comfortable, and well-located -- close to Taksim Square for food and nightlife, and near the T1 tram to Sultanahmet, where there are many, many things to see.
Irhan, our host, met us at the apartment. As the elevator was unfortunately out of service (he said it may need replacing), he volunteered to haul our suitcases up the five flights of stairs to his penthouse. He gave us a helpful tour of the apartment, eft a map, and later arranged for a cab back to the airport at the end of our stay.
One note of caution: Istanbul is built upon many hills, and Sea Tower is about midway up one of them. If climbing hills and stairs are hard for you, you will NOT be happy there. It's do-able -- my wife and I are both in our mid-50s, in decent shape (her more than me) and we managed pretty well -- but go into it knowing that unless you are willing to lay out w lot of cab fare, you will be doing some climbing.
All in all, a spectacular place to stay.