I would say radar/Battle of Britain (sort of interrelated) was one of two things that won the war, the other being the IJA pissing off the Europeans/US and forcing the Navy to attack Pearl Harbour.
Without the US there would have been many more casualties, prolonged the war, more costly for countries in the war (ie GB, Commonwealth nations, etc) and if the Allies managed to win, I think it would have been due to the Soviets and not the Western Allies. This would have led to a Soviet Europe, possibly a better economic situation for the USSR (since Germany is/was the economic center of Europe) if they could restrain themselves from taking all the factories to the USSR and otherwise ruining western Europe. In turn, the Soviet Union may not have fallen, we could still be in a Cold War, or worse have had one or more other World Wars after WWII.