One of Spielberg's most defining and seminal classics, this film represents everything his earliest work was and encompasses everything people now associate with Amblin as a brand.
While he had certainly tackled science fiction before this, he had never done so in quite an innocent and fairytale-like way. In showing audiences the arrival of this benevolent and loveable creature through the eyes of a child, the story took on a kind of mythic quality and completely subverted what audiences thought they knew about aliens in film.
It should also be noted that this was a much more minimalist film that Spielberg had ever made before. Rather than relying on setpieces or action beats, E.T. relies solely on character and heart to propel the story forward. It is the kind of sentimentality that Spielberg has been mocked for years, but it is crucial to remember just how ground-breaking and effective it was.
It is a big-budget blockbuster, whose thrill and entertainment comes from some of the most intimate moments. It was a pop culture phenomenon and it redefined what a Spielberg 'movie' was and could be.