Not enough is being said on the Soviet Union. That front--from a Russian perspective--was just one clusterfuck to the next. Remove Stalin before the military purges, and you have just made the Soviet Union massively more competent. Assuming this new leader has the competence of a monkey, he will listen to his intelligence experts who are telling him Germany is preparing for the war, then you have greatly shortened the Eastern front, since they now will be prepared for war, have enough officers, and be able to man the originally intended offensive line. If you throw in more successful Soviet-Japanese border skirmishes, then the USSR may even have more troops from the East brought up to the west in time to deal with Hitler. Even better, with this new leader, the prewar negotiations between the USSR and the Western Democracies goes better, and they form what effectivly becomes an anti-Nazi alliance. They were close to this IOTL, but for the wording of some sections. With no Molotov-Ribbentrop pact, the war becomes much, much shorter. That said, this scenario could lead to a war between the USSR and the Western allies.