Let's assume that the Germans decided to knock Britain out of the War before attacking the Soviet Union. Perhaps because they get the impression that Soviet forces have become too strong (clearly too many divisions and what the Hell kind of tanks are those?), they decide against Barbarossa after subduing Britain in late 1941 (combination Southern strategy, air build up and a more intense battle of the Atlantic).
However the Soviets have had their contingency plan to attack the West for some time and now that the Germans are relatively weak as a land force - Stalin decides he is strong enough to make his move in 1942.
I believe the Germans would be strong enough on the defense to absorb the shock with serious losses. The Soviets would suffer much greater losses due to lower efficiency. With access to world resources and maybe even aid from various countries afraid of Communism, I think Germany would have a chance to wear down Russia and win Lebensraum over the course of a few years.
What do you think? I'm fine with counter opinions or simply fleshing out the details.