Been playing in a Dawn of Defiance campaign set during the Legacy Era (surprisingly very little in the way of changes required to make it work), and the last official module we got through was Echoes of the Jedi, which was (to me at least) the worst of the bunch.
As for the goal of the campaign, not only is it to destroy the Big MacGuffin, but also to begin laying the groundwork for resistance against the Empire and what will eventually come together (after several years) into the Rebel Alliance, and short-term establishes House Organa as a viable resistance network.
In short, the campaign's climax shows that the Empire isn't all-powerful, and that you can not only fight the Empire, but that you can win. The players aren't going to be the ones to directly save the galaxy. They're the ones that are going to show everybody that the galaxy can be save.