This is an exceptionally well done making of the IRON MAN comic book series (of which I was a casual fan) that almost reaches the heights of SPIDER-MAN and BATMAN BEGINS. Only a lack of killer action and a powerful music score keep it from reaching those heights.
As others are saying, Robert Downey Jr. is terrific in the title role and brings humanity and believability to Tony Stark. The surrounding cast is great, with Jeff Bridges' look really lending itself to the antagonist role. Had the film's finale not been too short I would have given this top marks. Still, it's a great film and everything is set up for even better sequels (ala X-Men 2).
By the way, the very last moment before the credits begin is a line by Downey Jr and it brought the house down. Absolutely perfect way to end the film.
STICK AROUND AFTER THE CREDITS! If you don't know about the one final scene then where the heck have you been?