The difference is that the original trilogy appealed directly to the simplistic moral perspective of an America above reproach and always on the side of right in global geopolitics, whereas the much more subversive prequel trilogy stands in defiant counterpoint to the much more dangerously simplistic moral absolutism of the Age of Bush.
The original trilogy holds a special place in the bosom of American moviegoers precisely because we view ourselves comfortably in place of the Rebels. Americans revel in their historical construct as rebellious underdogs constantly at war against an easily identified and unquestionably evil empire. Hence, the reason most Americans love the original trilogy has much to do with placement of ourselves in the role of the inheritors of the mantle of the Jedi.
The problem is that the post-9/11 world meant Americans also were forced to identify themselves with the Jedi in the prequel trilogy as well, and we don’t like the face we see in the mirror. Let’s face it, the Jedi don’t exactly come off too swell in the prequel. This time around they are the guys in charge, and it is painful to watch them screw it up, especially when the way they hand over the keys to the Empire is so eerily familiar to a historical era defined by words like “signing statements” and “Patriot Act.”