Wow, ok. That's a word I would reserve for very few movies, and no Star Wars movie would make such a list for me (as much as I have a soft spot for the franchise despite its many shortcomings and duds).
I'm not looking to get in to an argument with you about it, but I would be curious to know which/some films outside the SW franchise that you would also regard as a masterpiece.
You really don't think ANH is a masterpiece? You're certainly entitled to your opinion but I think it is.
To me something does not have to be perfect to be a masterpiece. I don't think the Eroica is 100% perfect but it certainly qualifies as a masterpiece imo.
ANH is more involved than it may first appear. I read a long time ago that George Lucas hired quite a few experts on the world's myths and legends and their input was interwoven into the fabric of the story arc. As I wrote -it's not simple as it seems.
ANH absolutely obliterated the special effects bar when it came out. Watch Logan's Run (a movie which came out a few years prior and I enjoy very much) and compare what's going on on the screen.
Fantastic design decisions abound, such as making the rebel ships look aged and weathered instead of new and sparkly or populating the cast with veteran British actors to lend the story a true sense of gravitas.
Hell, to me John Williams brilliant score makes the film a masterpiece almost by itself. It's more than music - it's a character that inhabits the story, giving life to all it touches.
Of course - if Lucas had trusted his original vision and went with "Guido Starkiller" it could have sunk the whole thing.