The films borrowed a lot from previous sci-fi films before them, but did so in a pretty stellar way that hadn't been seen before.
You've got to take into consideration what CG has done to a modern audience with practical effects/puppets/layered stage design.
Nah, those movies aren't that great now, and even less so since Lucas pimped them a few times after the fact, but given how they changed mainstream sci-fi, they have to be considered some of the greatest films ever made.
You rarely hear anybody talking about Star Wars based on acting merit.
It's the fantastic nature of the original series as a whole that keeps it among some of the most cherished films of all time.
No, I'm actually not a Star Wars or Star Trek fan at all.
I'm just keeping it real.