Maybe I should be more clear. If he had focused on the area around Germany, honored his agreement with Stalin (if only for a while longer), and built up his empire, he would probably have prevailed. In the end, he just bit off more than he could chew, at least in the timeframe he chose.
Hitler had to attack when he did, Stalin was only getting stronger by the day, and many think Stalin would have attacked by 1943.
I would have gone straight to Moscow, and tried to get the Soviet government to collapse. Had Stalin been taken out, there might have even been a civil war between the Soviets, then the Germans could have divided and conquered.