Big Hollywood movies have been in the doldrums for months, which is why “Iron Man” arrives with such a metallic fanfare. This is the first real summer movie of the 2008 season; from here on out, it’s a weekly blockbuster fest, with Indiana Jones, Batman and the Incredible Hulk lining up in a distinct pecking order.

“Iron Man” is a funny combination, a movie from a Marvel comic book that doesn’t have anything like the usual blockbuster-movie casting. It works, in its quirky way, even if it doesn’t quite take off.

The hero of “Iron Man” is billionaire industrialist Tony Stark, a Howard Hughes type who’s made his fortune from weapons manufacturing. Stark is played by Robert Downey Jr.

Now, Downey is a fascinating actor, but you can imagine the collective intake of breath amongst studio executives when it was decided their megamillion-dollar franchise would be resting on the smallish shoulders of Mr. Downey. If Downey is on a somewhat short leash here, and he is, he’s still the unpredictable spark that keeps the movie going.

Stark is kidnapped by Middle Eastern terrorists, and must build a fantastic armored suit to escape. This is the birth of his superhero persona, which he develops back home after he renounces his past as a weapons-maker.

The film probably didn’t need an Oscar-winning actress to play Stark’s Girl Friday, Pepper Potts, but they got one in Gwyneth Paltrow. Even better, they got Jeff Bridges to play Stark’s business partner, one Obadiah Stane. They also got Bridges to shave his head and grow a hideous beard, and to have great fun in the role. Terrence Howard knocks around too, as Stark’s military buddy.

And as for the special effects — does anybody really care, other than they’re state of the art? They are.

The director is Jon Favreau, who also appears (slimmed-down from recent appearances) as Stark’s driver. Favreau’s probably responsible for the movie’s furtive humor, although after the enjoyable opening reels he never really gets the movie into a propulsive, headlong groove.

I enjoyed a great deal of it, although I’m a little puzzled by the nature of Stark’s invincibility — his body takes punishment that, with or without a protective suit, would crush an actual human being. Is this something we take on faith, or did the movie establish a supernatural quality that I missed?

But wait, this is a summer movie. These questions have to do with earthly logic, and are hereby banished for the next four months of moviegoing. See you at “Speed Racer” next week.