Eric says about the Star Wars prequel trilogy. Regardless of quality, those films are morally repugnant, and they thoroughly cheapen Anakin's transformation from perky grade schooler to evil incarnate. And I thank one of the commenters for linking to Patton Oswalt's brilliant routine on the subject.
That said, I do not think the films are uniformly bad. "Revenge of the Sith," for all its flaws, I maintain, was superior to "Return of the Jedi," although I concede that's not saying much. And while my early reaction to both "Phantom Menace" and "Attack of the Clones" was that they were irredeemable trash, I have come to believe that the former actually has several kernels of quality film in there that just aren't fully realized.
One of the recurring themes in "Phantom Menace" is the idea of symbiosis. Qui-Gon describes the midi-chlorians as symbiotic beings, living off our cells yet providing us with guidance from the Force. We are frequently told that both Jedi and Sith travel in pairs -- a master and an apprentice. Each needs the other. Beyond that is the suggestion that good and evil are never found alone. The light and dark sides of the Force are, in a sense, symbiotic.
And yet the great irony is that the Jedi, while teaching about symbiosis, seem blind to these relationships. The concept that evil might be nearby continues to escape them. They are slow to perceive the Sith threat. And Qui-Gon, for all his preachings, fails to acknowledge his dependence upon his padawan, Obi Wan.
All this is to say that there were a lot of interesting ideas and themes bandied about in the film that served the entire trilogy well. They were, of course, buried under some pretty crappy filmmaking. Lucas has a real knack for sucking the life out of actors. The principal actors of the prequel trilogy were much more talented than those of the original series, but Lucas still managed to make them all sound like middle-schoolers in a class play. And the film also gets very boring at times and generates needless plot holes. And then there's Jar Jar. But still, there's interesting material in here. Attention must be paid.
"Attack of the Clones," by contrast, is pure shit.