There is simply no question that TOS has a place in our culture that is unrivaled by any other entry into the Trek
franchise. TNG was ridiculously popular at the time of its airing, and still commands decent sales figures in things like DVD's. But the overall cultural phenomenon that surrounds TOS just isn't there for whatever reason. Oh, there are some elements of TNG that have made it into pop culture to a degree. The Borg and "resistance is futile" come to mind. But when people think Trek
, they still think Kirk and Spock. And, for that matter, William Shatner and Leonard Nimoy.