I bought this when in St Petersburg as I wanted to know more about the siege of Leningrad, and the most recent edition about that was too expensive. This has only a short chapter on the siege, but it is a fascinating book by a very good historian.
Overy provides a quick background to Russia before the war, notably the rise of Stalin, and the oppression of the 1930s. This establishes the political environment, and the relationship between Stalin and the Soviet people. Overy is good on the psychology of the dictator, notably his belief that he could read Hitler's intentions, which he posits is the reason for Stalin's infamous breakdown upon the invasion of the Soviet Union in 1941.
There's plenty in here I didn't know - I was very sketchy on the Eastern Front, which is why I was so interested in the book - and the biggest revelation was how badly the British, and French, fucked up a potential alliance with Russia in 1939. Invited by Molotov to send delegations to discuss an arrangement similar to WWI to intimidate Hitler from his expansionist ambitions, both countries sent envoys without sufficient authority to negotiate. This lack of commitment, and disrespect, frustrated Molotov, who responded promptly when Ribbentrop offered a non-aggression pact. Ribbentrop himself went to Moscow, the agreement was worked on in a couple of days, and almost immediately both Germany and Russia swept into Poland. Stalin was happy to have bought some time to rearm - he knew that Russia's military was no match for Germany's at that point, and indeed it still wasn't in 1941, when Germany unexpectedly broke the pact and invaded.
Overy is very good on the psychology of Stalin, although his attempts to understand his subject border on sympathy. He certainly represents Stalin's relationship with Churchill from the perspective of the Russian, who trusted Roosevelt far more. The battle descriptions are overviews, by necessity - there's plenty of other literature on Stalingrad, Moscow, Berlin, Kursk and Leningrad, and this is a summary narrative. The link throughout is Stalin, just as in Germany it was Hitler, but Overy doesn't overdo comparisons between the two.
The huge numbers involved on the Eastern Front are hard to appreciate. Overy talks of 500,000 men lost in a battle, or 3 million Germans captured - bear in mind that Britain had only 250,000 deaths in the whole war. The imbalance of the war is explicit - the Allies had relatively little action between 1940 and 1944, while Russia took the main burden. That they were able to do so, despite being technically outclassed for most of that time, was down to the huge manpower at their disposal, the brutal attitude towards the deployment of these men, but also to the tactics of some very able generals, notably Zhukov. The relationship between Zhukov and Stalin is a key one - the general was one of the few people who could contradict the dictator, and he has the same weight in this story as Kutuzov does in War and Peace. Both men saved Moscow, and therefore the country. Zhukov also saved Leningrad, and devised the plan to save Stalingrad. But when Stalin heard that Zhukov was claiming, after the fall of Berlin, to have won the war, he had him demoted - Stalin needed to be seen as the sole saviour of the country, although he was a poor military tactician.
Reading this has also been preparation for reading Vasily Grossman's Life and Fate, which I have since started.