Rod Serling's distinctive approach gave "The Twilight Zone" a unique character that will always keep it among the best-remembered of all classic television shows. Not only that, but it set high goals for itself, and it took a lot of chances - and not chances in the phony, trivial sense in which a lot of more recent series "take chances" by resorting to unnecessarily provocative or indecent material that actually guarantees them attention and acclaim.
"The Twilight Zone" took chances by experimenting with many different kinds of stories and material, and by aiming to provide high-quality entertainment while simultaneously giving you something to think about. As a result, there were a few episodes that didn't quite click, and that seem odd or even dull. But when it worked - as it did a great deal of the time - no television show then or now was more imaginative.
In a short review, it would be impossible to list all of the memorable episodes, or even to cover the full range of the kinds of material that it used. There were chilling episodes like "To Serve Man", which is often remembered by those who saw it decades ago, and there were thought-provoking episodes like "In the Eye of the Beholder", which was also imaginatively filmed.
Many episodes relied primarily on a well-written and well-conceived story, while others, like "The Invaders", relied heavily on excellent acting performances (in that case, by Agnes Moorehead). There were occasional light-hearted episodes like "Once Upon a Time", which was also a nice showcase for the great Buster Keaton.
It's too bad that these anthology-style series went out of fashion, because a number of them were of high quality. This one, in particular, stands well above its subsequent imitators. The best science fiction, like the best of any genre or art form, appeals to the imagination, not to the senses, and imagination is what "The Twilight Zone" was all about.