IRON MAN 2 — ★★★1/2 — Robert Downey Jr., Don Cheadle, Mickey Rourke; shown in both 35mm and 70mm (large-screen format); rated PG-13 (violence, vulgarity, profanity, brief drugs, brief gore, slurs, nude art); in general release

The biggest threat for "Iron Man 2" is not Ivan Vanko, the vengeful Russian inventor played in the movie by Mickey Rourke.

And it's not Justin Hammer, the avaricious arms manufacturer played in the movie by Sam Rockwell.

It's not even Senator Stern, the corrupt and manipulative U.S. politician played in the movie by Garry Shandling.

No, the film's biggest threat is expectations and over-hype. After all, it is a sequel to perhaps the most watchable of all the superhero movies made in the past decade — 2008's "Iron Man."

That film set the bar extremely high for all such films, much less for this direct follow-up. And let's not forget that both "Batman Begins" (2005) and "Spider-Man" (2002) both had even-better sequels — 2008's "The Dark Knight" and 2004's "Spider-Man 2."

"Iron Man 2" doesn't quite do better than its predecessor. It's too slow in spots, a little overstuffed with characters and story, and pretty set-up intensive. (This movie has to tease next summer's "Thor," as well as the eventual "Avengers" team-up movie.)

But it succeeds admirably in terms of being the kick-off for the 2010 summer movie season. It's a funny, exciting and even deceptively smart action-thriller with a few things to say about use of technology for destructive purposes.

Robert Downey Jr. reprises his role as billionaire industrialist and inventor Tony Stark, who continues to battle injustices and tyranny as the armored hero Iron Man.

His extracurricular activities frustrate Sterns and his fellow senators, who want Tony to turn over his arc reactor technology to the U.S. government so they can "weaponize" it.

But the worse news is that the arc reactor that helps keep him alive is also slowly poisoning him.

Yet Tony doesn't disclose this information to his closest friends — his Girl Friday, "Pepper" Potts (Gwyneth Paltrow), and military adviser James "Rhodey" Rhodes (Don Cheadle) — who are understandably worried about him.

At the same time, Tony has to fend off threats from both Vanko, who's using a more-primitive version of the same technology, and Hammer, who trying to create his own Iron Men.

As if that wasn't enough story and character content, director Jon Favreau and screenwriter Justin Theroux also introduce a mysterious new aide-de-camp, Natalie Rushman (Scarlett Johansson), and try to give enigmatic spy Nick Fury (Samuel L. Jackson) a little more screen time.

They don't skip on the action, though. There are couple of big battle sequences, including a loud, over-the-top finale that makes the film worthwhile all by itself.

The cast is terrific, helping steer the film through some rough spots. Downey makes Tony a charismatic, likable figure, even when the character exhibits some seriously selfish and self-destructive tendencies. And he's well-matched with Paltrow.

Rockwell is a real scene-stealer as the oily Hammer, and Cheadle is a more than adequate replacement for the bland Terrence Howard, who played that role in the first movie.

"Iron Man 2" is rated PG-13 and features strong violent content and imagery (gunplay and shootings, brawling, fisticuffs, hand-to-hand and martial-arts combat, fiery and explosive mayhem, vehicular mayhem, and violence against women), suggestive language and references (slang and innuendo), scattered strong profanity, brief drug content (use of drugs and antidotes, including an injection), brief bloody imagery, derogatory language and slurs, and brief glimpses of nude art (statues). Running time: 124 minutes.