So, a little backstory; before Episode 4 was released in 1977, movies were not what we think of today. In the decade before it was released, some of the highest grossing movies were downers. A Clockwork Orange, The French Connection, The Godfather, the Exorcist, Papillon...even Rocky ended on a down note. (Yes, Rocky 1 ended on a down note; he lost the match. That one was an anomaly until Rocky Balboa. But I digress.)
Star Wars brought hope into cinema. George Lucas gave us a story of triumph over adversity when all Hollywood thought we wanted was a gritty setting. George Lucas gave us high fantasy when Hollywood thought we wanted grim reality. And George Lucas gave us a world worth fighting for, when Hollywood thought we wanted a distopian view of things.
Because of Star Wars, special effects techniques and technologies advanced decades, which had stagnated since the 1950s. Any of you who have the original VHS or laserdisc releases of Episode 4 can see just how awesome the original effects were, compared to movies like 2001 a Space Odyssey or Planet of the Apes. Granted, these were done in 1968, ILM was dealing with pretty much the same technologies in the 9 years between. George Lucas wanted his movies to LOOK as good as the story he was trying to tell.
He also broke away with normal conventions of 1977; he went with a classical score instead of the disco or rock soundtrack that was expected at the time. Remember, in 1977, disco was king. But it is timeless because of it. A person who has never seen Episode 4 can watch it and not immediately think it's from the 70s. Don't believe me? Then check this out; it's a disco version of the opening theme.
(BTW, I had to change the video, but this is what 70s looked like to, in addition to what disco sounds like.)
This movie also started the trend of the summer blockbuster. Before this, if I remember things correctly, the biggest movies came out in the winter. With Episode 4's release on May 25, 1977, it began the trend of the summer blockbuster.
This movie began 36 years of fandom and cultural impact, and counting. We have seen books, tv shows, comic books, video games, fan fiction, fan movies, fan music, toys, and parodies. We've even seen a "religion"; the 2001 Jedi Census Phenomenon. Even lexicon from the film is known in popular culture; President Barack Obama mentioned the Jedi Mind Trick in one of his speeches.
Hundreds of authors, artists, musicians and film makers have been inspired by Star Wars. Seth Macfarlane, Kevin Smith, Seth Green, J.J. Abrams, and SO many others have been inspired by the Star Wars Saga. Hell, Abrams was tapped to make the next Star Wars movie, scheduled for release in 2015.
Star Wars has advanced technology, both inside and outside the film industry. Industrial Light and Magic was founded in 1975 by George Lucas. They are the biggest name in special effects today, and have advanced technology and techniques that filmmakers use today. We also got Pixar out of Lucasfilm. Skywalker Sound came from George Lucas, a set of tools used by both film makers and musicians now.
And lastly, there are VERY few people in this day and age who haven't seen at least one of them. I have met 2 people in 30 years. I have known over a hundred people (and I mean conversed with on a regular basis at one point or another. If I go with casual acquaintances, I've known more) in my life, and only 2 have never seen Star Wars in any way, shape or form.
Star Wars had its crap. Episode 1 and the Clone Wars cartoon comes to mind. Those are garbage. As is the New Jedi Order novels. Those piss me off. But no series of any genre has been as consistently good as Star Wars. No other fandom outside Lord of the Rings has the dedicated fanbase that Star Wars has. And yes, I know that the original Star Trek aired before Star Wars. But had it not been for Episode 4, Star Trek would have been nothing more than a scifi tv show from the 1960s.
Star Wars changed the landscape of the world. It has touched the world in ways most forms of media never could. No matter what Disney does with the franchise from this point on, what George Lucas brought us from 1977 to 2012 has touched the lives of many people, and will continue to do so for the foreseeable future.