While it's true that Vader being Luke's dad made for an arguably strong storyline, I think that there could have been better possible storylines, that could have led to an even better saga. I know it's hard to imagine such things because we've had 30 years with the whole thing revolving around Vader being Luke's dad. But that doesn't mean that a richer, wider universe couldn't have been created without that theme.

In my opinion, Yoda, Jabba, and the Emperor are terrific characters that enriched the movies tremendously. However, making so many of the main characters related was simplistic, and a better story-teller could have come up with a better theme. Of course, that's just my opinion.