You are correct in saying it works on its own. It could have easily been one classic, standalone film, admired for all time, in the way of "2001" and "Blade Runner." But, he chose to continue the story, which was also a good thing.

You know, on a similar note, I think that it really would be interesting if, when Lucas finally releases the ANH deleted scnes, some of our fan editors edit in the deleted scenes for ANH to make it more of an "'American Graffiti in Space" as Lucas' friends once called it.