I only saw star wars as an adult and even the original ones seemed overhyped and unimpressive. Bad acting, bad storyline. It's a "meh" series. I haven't even bothered to see the new Disney ones.
Alec Guinness, James Earl Jones, Peter Cushing, Harrison Ford--none of these are slackers. Anthony Daniels might not have much range, but he fit perfectly in the scope required of him. Mark Hamill was convincing as Luke.
The only weak link to me, bless her soul, might have been Carrie Fisher. And maybe a few bit-players. But the bulk of the show was carried by capable, if not excellent, actors.
My guess is that for its time the special effects were cool so people ignored the bad acting (especially) and the universe just built so much hype that it just became an institution few people dare to criticize openly. Also, popular with children + nostalgia :)