The original "Star Trek," created by Gene Roddenberry, was, with a few exceptions, bad in every way that a science fiction television show could be bad. [Leonard Nimoy] was the only charismatic actor in the cast and, ironically, he played the only character not allowed to register emotion.
Here's what I think: Most people weren't reading all that brilliant science fiction. Most people weren't reading at all. So when they saw "Star Trek," primitive as it was, it was their first glimpse of science fiction. It was grade school for those who had let the whole science fiction revolution pass them by.
Through-line series like Joss Whedon's "Buffy the Vampire Slayer" and Alfred Gough's and Miles Millar's "Smallville" have raised our expectations of what episodic sci-fi and fantasy ought to be. Whedon's "Firefly" showed us that even 1930s sci-fi can be well acted and tell a compelling long-term story.