On paper this book is dry and doesn't do much. But I discovered in late June, when you're actually on the ground and walking the streets in Istanbul using Rick Steves' book, this book comes alive, providing a huge about of historical detail for the sites you're walking past.
The book is a classic going back around 40 years, updated by Freely, and provides an important historical context for what you are seeing. I really was glad I still had it on the Kindle and could refer back to it because it told me a lot I would otherwise have missed.