Heads and shoulders above part 2, Iron Man 3 is a welcome change of pace for the franchise due mainly to the influence of Shane Black. There's snappy, sardonic dialogue, a somewhat disjointed timeline, book-ending narration, and some of the trappings of the cop-buddy genre of which he is the undisputed master.
Iron Man 3 also does things that on paper sound like a recipe for disaster: Tony Stark is out of his suit for large stretches, and a good chunk of the middle act he's teamed with a precocious kid. But they all work and it's these changes to the formula combined with a more focused plot and character beats that elevate it above the mess of part 2 and into the realm of the superior comic book films.
Throw in a solid set of villains with a nice twist, and some fantastic action set pieces and the bar has been set high this year for the summer action tentpoles to come.