The firestorm caused by the revelation of the Mandarin character in Iron Man 3 is funny to me. Though it is kind of sad that one of the best Marvel movies gets sidestepped for it.
Ben Kingsley was presented as this frightening, intriguing character. But it wouldn't have been any more interesting on it's own, played straight, as opposed to what the final product was. Killian flips the whole thing around and makes for a much more entertaining finale.
Two things that drive it home for me: Tony Stark's reaction to discovering the truth, as played by RDJ. It was perfect. He is as stunned as we are, you can see the confusion and frustration run through his face before he readies his gun and demands answers from Trevor. Second, the fact that Trevor's Mandarin is still Killian. People claim Guy Pierce's character was bland, that Mandarin was great until the twist, etc. But who gave the actor his script? Who created the role Trevor was cast in? How does that take away from the menace the Mandarin was in his televised threats, or take a way from the previous bombings which AIM, Killian, the Mandarin are responsible for? To me, it enhances the movies antagonist.