NSA mass surveillance has not led to one single terrorist being sentenced in a court of law. Not one.
NSA did not manage to foresee the Russian annexation of Crimea. And it does not seem to give western leaders any assistance of substance when it comes to predicting Russian moves in eastern Ukraine.
NSA did not manage to predict the sudden rise of IS in Iraq and Syria.
NSA apparently had no clue when it came to the uprising in parts of the Arab world during the Arab Spring. And the agency seems to be of little help when it comes to keeping the western world in touch with developments as that spring turns into autumn and winter.
NSA do, however, manage to keep track of the telecommunications of millions and millions of ordinary people–who are not suspected for doing anything wrong or dangerous at all. And the NSA has succeeded in causing resentment among some of the US most important allies.
I feel sorry for the US taxpayers.