Vaderisnothayden said:
Xizor is a Mary Sue because the story goes "Look at our cool villain, look he's so cool he can rival Darth Vader and get fresh with Leia."
So... you'd be more compelled by a villain who isn't cool, doesn't try to challenge the status quo, and leaves the heroes alone? (and in case you forgot, he was pwned by his Darthness and Leia kicked him in the nuts)