The opening crawl has a lot to answer for. The story's really not about a trade dispute, but first impressions are important. The crawl should have mentioned less politics and more about a peaceful planet being surrounded by an armada of alien battleships, threatened with invasion, and two brave Jedi Knights being sent in alone to the rescue. That stuff is in there, but it gets overshadowed.

I agree with you that a lot of the success is down to Ralph McQuarrie and John Williams, though you ought to have mentioned Ben Burtt as well ;o)