Flawed superheroes are the best kind.
When Tony Stark first arose out of the ashes of captivity in the original Iron Man movie, he became conflicted and had to recalibrate his moral standing.
Iron Man then realized he had to stop letting pride and selfishness get in the way, whether by allowing others (War Machine in "Iron Man 2") to help, or making the sacrificial play to help his team (like carrying the nuke through the black hole in "Avengers").
Seeing a superhero overcome character defects and internal issues is just as satisfying as watching said superhero destroy the bad guys. In fact, it's no coincidence that those things often go hand in hand.
Stark tells the heavy "Iron Man 3" tale as a broken man (on this note, the stinger after the credits is awesome). And what ensued was a path to mending his physical and mental states while trying to determine if the weight of the consequences of his actions is worth the possible pain. "Iron Man 3" is a big venture in style and direction from its two predecessors at it takes a good, long look at Stark, the man. It won't feel quite like the other Marvel movies, but that's okay.
There is a reason Disney and Marvel started Phase 1 of this superhero saga with Iron Man; it's the same reason they started Phase 2 with Iron Man.
And that is Robert Downey, Jr.
Sure, Downey was witty when he needed to be. He was pompous on occasion, especially when he figured out what the bad guys really are all about or when he came up with solutions for getting out of sticky situations. In a lot of ways, he was the same character we've come to know and love.
But in "Iron Man 3," which takes place shortly after "the events of New York" (an allusion to "Avengers"), Stark is dealing with different types of problems, and Downey was fully capable of showing range with the different sides to the character. Stark has a full-on case of post-traumatic stress, which induces panic attacks when he dwells on New York too long. For once, the seemingly unwavering, unstoppable Tony Stark shows vulnerability, beautifully captured by Downey Jr.
Stark learns to cope with this, partly with the help of a quizzical little boy he meets (their exchanges are some of the best in all the Iron Man movies) while on a trip to discover the truth about The Mandarin - Iron Man's prime enemy in the comics - and his minions. Without spoiling too much, after Stark gets the help he needs and deals with these issues, he starts to lead everyone to believe he is ready to hang up the suit for good. Suffice to say, this was a weary, testing, even solemn moment as Iron Man's future was hanging in the balance.
While the focus of "Iron Man 3" was on Stark, the rest of the film was just as heavy. Footage of terrorist attacks in pockets throughout the world (that hit really close to home with today's real world) paint the despairing picture of The Mandarin's work. The Mandarin is a scientist who gains his power through his 10 rings (which inspired a name for the terrorist group alluded to in the original Iron Man movie). While the science of his powers aren't explained enough (they're also not nearly as diverse as the comics), The Mandarin proves to be one of the most formidable enemies. Several great action scenes depict just how evil the bad guys really are; there were true glimpses of anger, rage and hatred in their faces that made everything seem a little more real.
Clearly that is what director and screenplay writer Shane Black (his most famous work was on Lethal Weapon 1 and 2) was going for. From the outset of the film, there is a gritty undertone and darker cinematic work that give the film a far less colorful feel than the other superhero movies. The camera work was tighter and, at times, more calculated, which in some ways was bad because the Marvel movies did a good job of being clear and motionful and not quick and overly edited like most action movies.
There is a cool visual skydiving scene that's worth mentioning, especially because a lot of it was real stunt work and not simply done in front of a green screen. Kudos.
Also worth mentioning (but not spoiling too much) is the fascinating way Stark tricks out his Iron Man suits, which makes for some interesting strategics and eye-popping action scenes. No, Stark isn't in in his suits as much as before (half the time his suits were malfunctioning prototypes), but he still has a few awesome fighting scenes.
Gwyneth Paltrow, who gets wonderful, extensive screen time in many different venues, shines well in her multi-faceted role as Pepper Potts, which gets expanded in ways she hasn't had to this point. Don Cheadle's War Machine (which turns into Iron Patriot) gets delightful extended time with both Stark and Iron Man as their friendship strengthens.
"Iron Man 3" is different; it won't feel the same at all. But "Iron Man 3" is amazing nonetheless.