I think that the ending of ROTS was quite original. I expected for Anakin to become evil because of the visceral power of the Dark Side, or because he wished to save his wife, or because he hated the Jedi for being incompetent fools. Any one of these, or a combination thereof, would have been a predictable ending to the trilogy.

What we got was Anakin choosing to protect the life of Palpatine against an attempted murder, with the stated purpose of allowing for the justice system to decide Palpatine’s fate, and the unstated purpose of using the trial to discover if Palpatine actually has the knowledge to save Padme’s life. Immediately upon doing this, he abandons his plan to turn Palpatine in, apparently deciding that he himself must be evil now and a disciple of the most evil man in the galaxy, with his only stipulation that Palpatine save Padme. Nevermind that he has slaughtered a whole tribe of sentient beings and killed countless beings in the Clone Wars; now that he’s party to a murder in self defense, he decides that there are no backsies and is all-in with this evil thing. Then Palpatine admits that he doesn’t know how to save Padme, and Anakin doesn’t do the obvious thing and arrest the chancellor then and there. Instead he murders children, and after Padme is dead decides there’s nothing left to do than to become Palpatine’s lackey for 20-odd years. No reason for his turn rings true, not even his mad lust for power at the end since he believes Palpatine, for all his deception, is still his closest friend. In the end, Anakin turned not because he was evil, but because he was confused and stupid.

That’s an ending that I didn’t see coming, that’s for sure.