Whoa, that is unusual. While I have grown to hate the Star Wars franchise, I adore Lord of the Rings and many of the Star Trek tv shows (though not all of them)
I have to say, these recent daily Dart threads are a good way of finding out who the extremists are around here, lol. Often in very surprising ways. While there's nothing surprising about any specific personal taste, to be on an RPG specialist forum & then have someone declare zero interest in all of those three series is remarkably odd.
To answer the thread question, it has to be the first one (which was later relabelled episode 4). The main problem with Star Wars is that it doesn't actually have a universe to expand into, each movie is just a retread of the war between the Alliance versus the Empire, which would be ok if the Empire weren't technically defeated at the end of the first movie. At least as far as they ever needed to be.
So instead of each episode providing a new angle of the universe to look at, it instead tries to be a Bond movie and just repeats itself with different gadets with different environmental backdrops (Desert, water, jungle, space station, snow etc). While this works for Bond, who's job never chages and is self-titled about an individual doing a specific job, it doesn't work for Star Wars because there's only so many times you can see the empire and/or it's leaders get destroyed/killed. To have thewhole universe to play with (like Star Trek) and then to do pretty much nothing with it just makes the descriptor for the series be "Myopic".
This is made even worse by the cock and bull way the characterisation is handled throughout, whereby each series and even episode can have a completely different cast-list and motivations, so there's no one person to really root for throughout. Ironically, the most prominent characters have been the bad guys, with Darth Vader's character getting six films and The Emperor getting four films, both of whom have a greater screen presence and in depth characterisation far in superior to the good guys with the same screen time, such as Obi Wan, Solo or Luke. Who exactly is Star Wars about?
Etc.