I read some of the comic run of Iron Man, but it's really been the movies that made me that much more of a fan of Iron Man. That's due in no small part to the amazing job that Robert Downey Jr. has done portraying Tony Stark. And in Iron Man 3 I think he was able to make the character grow beyond what we've seen in the previous two films as well as in Avengers.
I think the big theme of this movie was that Tony was human. He may have this amazing intellect and fantastic skill at building things, but unlike some of his fellow Avengers, Tony is just as frail as any other man. Still, as "The Mechanic", Tony has been able to do things that are truly astounding.
Tony has had the armor at his beck and call through the whole movie series. Seeing him in a position where he has to rely on his wit more than the power of the armor has given his character that much more depth. Especially when he's faced with a foe like Killian who possesses an intellect that's on par with Tony's.
The Mandarin fašade was interesting. It harkened back to the Ten Rings plot point from the first Iron Man. But I have to agree with Bill, that the Mandarin character from the early Iron Man comics was very much a charicature that was a product of it's times. And the concept behind the Mandarin's powers doesn't really work in the world that Marvel Studios has established. At least not without a serious backstory that could bog down the flow of Iron Man 3.
I can't say that I know that much about the Extremis storyline from the Iron Man comics. Or if Aldrich Killian had been established in the comics. But I think that if you're going to have a villain who can come across as credible in a film like this, they have to do so from the shadows. AIM works better in the movie universe as a think tank / research organization that's engaged in questionable research to put itself in a position to get government contracts, etc.
As for nerdy Killian from the 1999 scenes in Bern? That was a bit over the top. As was Happy Hogan's look at the time. But I did appreciate the fact that they worked Yinsen from the first film into that scene.
And in the whole mix of things, it turned out that the speculation regarding the Wasp making it into the movie was just that. It would have been nice to see some possible future Avengers introduced in this movie, but I get the sense that doing so might have bogged down a pretty dense movie.