IRON MAN — *** 1/2 — Robert Downey Jr., Jeff Bridges, Gwyneth Paltrow; rated PG-13 (violence, torture, profanity, brief gore, brief sex, slurs, vulgarity)

Like most, if not all, superhero origin movies to date, "Iron Man" ends with a bit of a clank, a clunk and a thud.

That includes a rather rushed and unsatisfying wrap-up sequence that is clearly setting up things for a sequel, though given how good the rest of the film is, you definitely want to see such a thing anyway.

And besides, the whole thing starts with such an explosive rush that you can forgive what few storytelling hiccups there are.

In fact, this exciting, enthralling action-thriller is certainly the best comic book-based movie since the second "Spider-Man" film, which is high on a lot of fans' lists for such things.

Much of this particular film's appeal has to do with the initially controversial casting of Robert Downey Jr. as the title character. He plays Tony Stark, a wealthy inventor and munitions manufacturer.

While on a trip to the Middle East, he's kidnapped by terrorists and is critically injured — ironically — by one of his own weapons. The only thing keeping him alive is an advanced electro-magnet that prevents shrapnel from reaching his heart. He also builds a suit of robotic armor to help free himself from captivity.

And when he returns to the United States, Tony announces his plans to quit making weapons of mass destruction.

As you might guess, there are many people questioning his sudden change of heart, including Tony's best friend, James "Rhodey" Rhodes (Terrence Howard), his gal Friday, Virginia "Pepper" Potts (Gwyneth Paltrow) and his mentor, Obadiah Stane (Jeff Bridges), who isn't pleased by this development.

What they don't know is that Tony is building another suit of high-tech armor so he can clean up "messes" caused by use of his weapons and technology.

It's a fairly heady concept for a summer movie, though director Jon Favreau ("Elf") and four credited screenwriters keep it from becoming overwhelmingly heavy-handed and bleak.

The film also has its share of goofy humor, and a tremendous asset in Downey's winning personality. As Tony, he's very likable, which isn't easy. His selfish character could have been completely unsympathetic.

The good supporting cast includes his fellow Academy Award nominees Howard, Paltrow and Bridges. And it's fun to see Bridges playing one of the film's heavies.

Sharp-eyed fans of the Iron Man comics may notice a few "Easter eggs" scattered throughout the movie, such as references to international SHIELD agency, a villain named the Mandarin and another armored hero, War Machine. And that's filmmaker Favreau himself, playing Tony's bodyguard/driver, "Happy" Hogan.

"Iron Man" is rated PG-13 for strong scenes of violent action (shootings, explosive and vehicular mayhem and scenes of armored combat), a couple of sequences depicting torture and interrogations, scattered profanity, brief gore, a brief sex scene (implied), a few derogatory slurs, and a brief vulgar reference. Running time: 120 minutes.

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E-mail: jeff@desnews.com