As others have said no Stalin really changes the game. Stalin gets a lot of credit nowadays for dragging Russia kicking and screaming into modernity, but in many ways he was the worst possible man for the job. The damages the Purges alone did to the Soviet Union cannot be understated. Without his purges there are the obvious butterflies (some very good administrators, military men, and scientists don't get killed), but in the long term the USSR gets another advantage. The Purges killed many low and mid-level bureaucrats, some of whom would no doubt have been very skilled. These men would have probably risen to the upper echelons and been able to apply their skills to running the government. So instead of conservative and fossilized men like Brezhnev we could see more dynamic leaders, which is pretty key in stopping OTL's stagnation.