One has to remember that we tend to view the "original" movies through the eyes we did when we first saw them. Most of us were children or teens when we saw them and, frankly, children have lower standards. I tried watching them from an adult point of view, which was quite difficult, but I realized that from that viewpoint, those movies are not all that great. The droids are annoying. The ewoks are far more juvenile than Jar Jar, something I never though possible.
Secondly, the first set of movies has a set of plots that are simplistic and naturally geared towards younger audiences. The second set are really political thrillers that were, unfortunately, made in a style to entertain young males (an inherently flawed concept).