It couldn’t have taken long for the “Iron Man 2” assembly line to get fired up after the surprise success of the first film, which was a solid blend of competent action excitement and irrepressible snark.

So I guess we can be grateful that the sequel doesn’t come off entirely as some kind of blockbuster mill progeny — shiny and fun on the outside with a genetically degenerative pair of hips.

Screenwriter Justin Theroux (“Tropic Thunder”) delivers a film that is very much in the spirit of its predecessor, which he did not write, but it’s more convincing in the big picture than it is in the details. Director Jon Favreau displays less enthusiasm for the material, too — perhaps he was more concerned with perfecting his enlarged role as pudgy assistant Happy Hogan.

But then there’s Robert Downey Jr. — a film’s godsend personified if there ever was one. Downey Jr. ratchets up the fun factor of everything he appears in, and without his presence, the “Iron Man” franchise would still be just a second-tier Marvel entity.

This time around, it’s six months after the events of the first film, and Tony Stark — (Downey Jr.) is feeling pretty good about the state of world affairs. He claims to have privatized peace, developing a technology that has ensured no rogue countries want to mess with the United States.

The government wants control of Stark’s Iron Man suit, but he won’t give it up, and in a massively entertaining self-aggrandizing speech at a Congressional hearing, he tells a sniveling senator (Garry Shandling) that he’s the only one who could’ve developed such a technology.

Too bad for Stark there’s a hulking Russian cliché copying his design a couple continents over — Ivan Vanko (Mickey Rourke), who has a history with the Stark family. This bit of stunt casting just doesn’t make much of an impression, as Rourke seems better at laying on a thick accent than actually appearing menacing.

The film’s got plenty of other irons in the fire though, with the fantastic Sam Rockwell as spray-tanned Tony Stark wannabe Justin Hammer, a beefed-up part for Gwyneth Paltrow as Stark’s assistant Pepper Potts and Scarlett Johansson and Samuel L. Jackson as a pair of characters who are shoehorned in for the purpose of generating excitement for the upcoming “Avengers” spin-off.

Don Cheadle, who replaces Terrence Howard as Lt. Col. James Rhodes, is a better fit for the character, and he gets to display his inherent badassness often as he suits up alongside Stark.

“Iron Man 2” keeps its tongue firmly planted in its cheek, which helps set it apart from the usual crop of self-serious comic book films. It maintains a brisk pace that keeps it engaging, but it’s often at the expense of truly satisfying character resolutions.

But what will likely be the biggest letdown for fans is the film’s lack of newness — “Iron Man” vastly exceeded its minor expectations and was carried along on waves of exhilaration. “Iron Man 2” doesn’t get that benefit.

Good thing Downey Jr. looks like he’s having a blast — as usual. His enthusiasm and charm is infectious, and it can turn a merely capable film into one with superhuman entertainment powers.

Screening Times

Hollywood Theaters - Spotlight 14

1100 N. Interstate Drive, Norman

12, 12:30, 1:20, 1:50, 2:20, 3:45, 4:15, 4:45, 5:15, 6:45, 7:15, 7:45, 8:15, 9:15, 9:40, 10 10:40 p.m.

Warren Theatre

1000 S. Telephone Road, Moore

12, 12:30, 1:30, 2:30, 3, 3:30, 4:30, 5:30, 6, 6:30, 7:30, 8:30, 9, 9:30, 10, 10:30, 11 and 11:30 p.m.