I found the film very respectful of its source material--unlike many comic book adaptations that wink at their origins--and surprisingly faithful. Southeast Asia circa 1963 was easily updated to Afghanistan today. It has a nice mix of humor and action. Robert Downey Jr. plays Tony Stark perfectly as a suave mix of Howard Hughes, Bill Gates and Errol Flynn. Stark has a satisfying emotional arc from insouciant weapons dealer to conscience-stricken knight, and Jeff Bridges plays the villain Stane with a great combination of warmth and menace. You'd believe he was your best friend until the second he stuck a knife in your ribs, and might even believe him when he said he regretted doing it.
All in all, I'd call it one of the best comic book movies ever and, more importantly, a movie that audiences completely unfamiliar with Iron Man (admittedly a second-tier character) will enjoy. My only caveat is that it's fairly violent; Iron Man doesn't hesitate to kill bad guys who deserve it, and though the deaths are mostly bloodless and off-screen, they might be too much for young or sensitive viewers.
That's all well and good, but I don't normally post movie reviews unless I have ulterior motives. In this case, I noticed an end credit acknowledging the work of four men in creating Iron Man: editor Stan Lee, (who makes his customary cameo in the film), writer Larry Lieber (Stan's brother, who wrote Iron Man's early stories), Jack Kirby (who I believe designed Iron Man's first armor), and ... Don Heck, Iron Man's first artist. I wrote about Mr. Heck in April, citing him as my personal example of an artist whose work I didn't appreciate until my critical eye had matured. Heck's loose brushwork was perfect for the Swingin' Sixties James Bond vibe of the early Iron Man stories. It was nice to see a maligned artist get his deserved due.