CO asks a great question: why are these movies so timeless and popular regardless of culture, and shouln't i be bored with them by now? to be sure, the mythic elements are resonant across civilizations and definitely help to make star wars accesible to all, but it's only a formula. few other films employing these tropes come close to the emminent watchability of the OOT.
ultimately i think it was a complex of variables:
1. mythic goodness
2. fantastic chemistry between actors (lucas sensibly spent a great deal of time on casting)
3. great writers helping lucas out
4. he borrowed the coolest stuff that kids from his era grew up loving and imitating on the playground, and blended all of these very FUN elements with "impeccable taste and panache" (westerns, flash gordon type serials, monster movies, war movies) into a delicious cinematic souffle. they're so much FUN to watch, and i think that accounts for a lot.
5. most importantly, he was plain lucky. everything just clicked while making these films. he had the right people surrounding him at the right time and the right place and he was a hungry, young artist desperate to prove himself. everything fell into place, and to his credit he birthed a work of genius.
with the prequels lucas was far from being a desperate artist. the primary concern was no longer the manufacture of profoundly artistic films; he was more concerned with advancing the technology of movie making. being surrounded by yes-men probably doesn't help. the emperor wears no flannel ... ewww.