I saw Iron Man 3 a couple weeks ago, and as a movie itself, this blows STID blows it away.
This. Iron Man 3 was a totally enjoyable experience while I was watching it, but it really wasn't that memorable and a LOT of things bugged me afterwards (and I'm not one of the ones who took offense to the Mandarin reveal). That movie really had no heart.
It's not like Iron Man is incapable of heart, either. The defining moment for that whole franchise is the press conference just after Tony Stark was rescued, when he says "I saw young Americans killed by the very weapons I created to defend them and protect them," and you see the shame cross his face. And then later in the movie when he's talking about realizing his destiny. Those were great moments of pathos, and the biggest reason why the first Iron Man stands head and shoulders above 2 and 3, because all attempts at pathos in those movies felt really forced.
STID is so much better than Iron Man 3 for the same reason: the pathos in the character work feels really real, and just works. It has a heart (not to mention some fantastic action and lots of humor to boot).