The Germans had a couple of opportunities to win WW2. The first was to eliminate Britain from the war, by either winning the Battle of the Atlantic , thereby cutting them off from food and supplies, or to win the Battle of Britain, which would then lead to Sealion. With Britain out of the war, the US would find it virtually impossible to perform a land invasion of Europe or to carry out air attacks on Germany.
The alternative was a swift victory over Russia, and then they could reinforce Italy, North Africa and France to prevent an attack from those directions.
By early 1943, with the defeat at Stalingrad, and with the loss of enormous amounts of men and machinery, and with the breaking of the wolfpacks and the amount of men and munitions moving from overseas to Britain the writing was on the wall for Germany. The manufacturing power of the US and Russia, churning out tanks and planes in their thousands meant that regardless of the quality of German armaments, they couldn't be supplied in in enough numbers to make a difference. I think it was Stalin who said that quantity has a quality all of it's own; this was certainly true in WW2.
If the Germans had managed to create an atom bomb and a method of delivery, that would have changed the course of the war. But other than that, I think that from mid 1943 onwards, it was simply a case of when and not if, and also a question of how Europe would look after WW2 finished.