Luke Skywalker's story is a retelling of Nuada Airgetlám, the first king of the Tuatha de Dannan, in a sci-fi fantasy setting.

Because there is a cultural Zeitgeist about this even if it is not well known, it had a better well of mythology to pull from and therefore it had more impact than the sequels and prequels which were repulled from the saga of Luke Skywalker in the original trilogy.

I think the lack of depth for all of the movies since the original trilogy come from the fact that they do not tap into any other sources than their own source, leaving them all feeling hollow and sterile compared to the original.