MarthWMaster said:
I think that is because Vader has a lot more dimension than most of the other protagonists in starwars. He is more machine than man, Why? He has a chip on his shoulder yet saves his son in the end. Why? etc.
Vader is not the most 3 diminesional character around, but as you noted, he is rather compelling.
Contrast this with the whiney, snot nosed and incestuous brat that is Luke Sky walker, and you can easily see why the dark side likely has a larger following. People like Han Solo who shares much of the same mysteries as Vader, not Skywalker.
At least Rowling attempted to make her protagonist Potter more compelling, but ultimately he is just as emo as Skywalker.
Frankly, with as much 'good' as Lucas has done for the franchise with his last three films, he may as well just stop being so draconian and let others run within the set background without constraining creativity to exclude a possible antagonist victory.
Being bad was one of the reasons why KotOR II was so good.