Well, that didn't take long. Everything fun and terrific about "Iron Man," a mere two years ago, has vanished with its sequel. In its place, "Iron Man 2" has substituted noise, confusion, multiple villains, irrelevant stunts and misguided story lines. A film series that started out with critical and commercial success will have to settle for only the latter with this sequel. Robert Downey Jr.'s return as Tony Stark/Iron Man will assure that.

For a film riding a wave of unbridled achievement from its predecessor, "Iron Man 2" begins with a curious sense of panic. Characters all talk at once.� Hesitant story lines launch in all directions. The soundtrack and music clang away, but onscreen little happens until a big set-piece at a Grand Prix race nearly 20 minutes into the movie.

Downey's Stark, the Howard Hughes-like creator of the Iron Man's software and hardware -- and its embodiment when he dawns the flying iron suit -- is suffering from both megalomania and a blood toxicity condition. These seem to be leading Stark into severe mental instability.

Other plot lines concern a Congressional hearing and a nasty Senator (Gary Shandling), a crazed Russian inventor (Sam Rockwell), a dishy new assistant (Scarlett Johansson) as a rival to his Girl Friday (Gwyneth Paltrow), a demented Russian inventor (Mickey Rourke with tattoos splayed across his body), psychological issues involving Stark's late father, a sidekick (Don Cheadle) who betrays Stark and the deterioration of Stark's corporation.

And what is at stake here? The fate of the world? The emergence of a new superpower? No, it all seems to pivot around who'll win a new Defense contract. Wow, there's an emotional grabber.

A new writer, actor Justin Theroux, must have "Cut To:" installed as a default in his screenwriting software. When in doubt, his script cuts to a new place -- Moscow, Monte Carlo, Malibu -- character or situation, not all of them credible or logical.

An actor as formidable as Samuel L. Jackson doesn't even show up until the movie feels like it's winding down. He wears an eye patch and an air of uncertainty. Now who is he supposed to be? Oh, he's Scarlet Johansson's real boss, and then she turns out to be Cat Woman only without the feline suit. She struts through the film in various stages of dress and undress, which may be the best thing about "Iron Man 2" for its younger male fans.

What made the original film so, well, original, was the notion of a superhero as a conflicted individual with enough complexes and mental crises that saving the planet became a sort of stress-relief valve. Now he's borderline psychotic. Not that Downey has any qualms about tackling messed-up bad boys, but the film never makes clear whether he's just being Tony or really cracking up.

The CGI fight scenes quickly become tedious, their outcomes never really in doubt and the mechanics rather clunky. The sight of metal men smashing each other about without drawing any real blood is more reminiscent of the sandbox games of a child with his play toys than any movie magic. That actually was true of the first movie as well, but one overlooked it because Tony's prickly personality so dominated the action. Here Tony has to fight too many over-the-top characters for audience attention. He loses that battle.

Visual and CGI effects are the best and worst thing about "Iron Man 2." The film relies far too much on them. They catch you up in the action but, unfortunately, nothing else does.

Opens: May 7 (Paramount Pictures)
Production companies: Paramount Pictures and Marvel Entertainment in association with Fairview Entertainment present a Marvel Studios production
Rated PG-13, 124 minutes