'Iron Man' is shaping up to be not just a hit, but a good movie on top of that. Robert Downey Jr. is perfect for the role -- well-versed in the ways of the world (as a superhero must be), but still just a kid at heart. Should lend Iron Man the gravitas needed to be taken seriously without alienating the kids the movie will be meant for -- think Batman sans all the moping around.
Jon Favreau is getting knocked for his unproven ability to direct (he's done some TV but that's it), but check out the clip -- it's perfectly shot, works as exposition (it explains [non-verbally] how the suit enables Stark to fly), and one can only assume the timing of this plot point is right on. Looks like Favreau not only has the chops needed, he's got a natural affinity for the material -- and that can't be faked.
As for the intangibles, the 'learning to fly' clip had me hooked -- it's just plain good, plays real, and gets you to know and like the protagonist. All in all, pretty effective film-making.