The Gestapo actually wasn't that good at spying. The German people were, however, quite good at turning their neighbors in to the Gestapo.
Which means Gestapo was good at spying. The indicator is whether you get results, after all, not whether you get them because you're smart or scary.
There's a lot of myth concerning the Nazi police force. It's unfortunate that even today people repeat it without thinking.
"He who thus domineers over you has only two eyes, only two hands, only one body, no more than is possessed by the least man among the infinite numbers dwelling in your cities; he has indeed nothing more than the power that you confer upon him to destroy you."
Tyrants stay in power, not because they're stronger than their very source of power, but because they're good at building myths. A nation, company or any other organization is nothing more than a myth shared by its members. And the myth of the Third Reich is so strong it still persists, long after its embodiment is gone, as a kind of ghost nation. Time will tell whether Hitler will take up permanent residence in our collective pantheon along the Caesar's and Napoleon.