However, it's worth remembering that the Star Wars movies were meant to be regarded as individual installments in a much larger story. The whole point of the opening crawl in ANH was to recreate the experience of going to a Saturday morning matinee and being brought up to speed on what happened last week in your favourite serial. As such, it's fair to say some of the movies are better than others (just as someone can say a certain chapter in a novel is better or worse than another chapter), but in the end all the movies make up the grander narrative that is Star Wars.
I must say, though, that there's something to be said for leaving some "story" out of the story to create that little bit of mystery (not unlike Tolkien hinting at the historic events of Middle Earth in LOTR, but not elaborating upon the point). In that sense, it was kind of fun not knowing exactly what preceded ANH; it was fun imagining the events for yourself.