I would think the major gripe with the "twist" is that a major villain from the Iron Man universe essentially doesn't exist. I suppose a true Mandarin could show up later, but I think that ship has sailed. I don't see why Kingsley's version couldn't have had the magic rings. I think the depiction of AIM fit very well in the movie Marvel universe. I don't think you could have brought in a character like MODOK into the movie. I think they did a good job with most of the Extremis elements as well. I'm not sure I would have gone with the Killian arc as they did though. Overall, I think the villains have been the weak point in the Iron Man trilogy as a whole.