The ebb and flow of debate about Stalin's Russia is brilliantly captured in this book. Chris Ward conceptualizes the field in a clear and helpful way, offers a synthesis of the vast secondary literature in the area, and provides evaluation of the key issues at stake. This second edition includes the necessary updating, the provision of more maps, and a new chapter on foreign policy.
If you ever need to understand the English-language historiography on the Soviet Union under Stalin, you could do a hell of a lot worse than this book. Read up on the books that have been published since this one and you should be set.