Robert Downey Jr. is at the peak of his talents. Again.

Robert Downey Jr. preemptively spits out the "P-word," as he calls it, at least nine times as we talk, with varying notes of irony or bitterness. The first time he says it, he's talking about his new film Kiss Kiss, Bang Bang.

"My honey read the script first," he says, referring to his new wife, Hollywood producer Susan Levin. "She was having this kind of Vesuvius-eruptive laughter. And I thought, That's weird. She's not laughing at any of my jokes. So I read the script and I thought, It's got so much potential - potential, that word, man - every time somebody says that it makes me want to say, 'Hey, why don't you go jump off the Santa Monica pier?'"

By now, audiences are probably just as sick of hearing about the actor's potential as is Downey himself. His career has been one long, exhausting cycle of flameouts and comebacks, highlights and mug shots. And yet, in Hollywood, the Downey what-if scenario remains every bit as alluring and enduring as Washington's What if Clinton hadn't done Lewinsky? If Clinton had kept his nose clean, we think, maybe we wouldn't have had to endure Bush. If Downey'd sobered up, the logic goes, maybe we wouldn't have had to endure Matthew McConaughey.

It's been twelve long years since Downey's Oscar nomination for Chaplin, and decades since his father, the Village's wild-man filmmaker Robert Downey Sr., cast him in the underground film Pound. It's been five years since Downey got out of prison, four since he got booted off Ally McBeal, and almost three since he sobered up - with the help of young love (Downey's 40, his wife is 31) and "a high-end diva assortment of things I need to do to stay out of my own way," he says, including daily kung fu training and "the Big Gulp AM/PM coffee mug filled with tea bags and Coffee-mate."

Today, the cleaned-up actor is buff and busy. Following the Eddie Murphy Ten-Step Career Recovery Plan, he's just spent the afternoon recording voice-overs for a Disney kids flick, The Shaggy Dog. Then he picked up his 12-year-old son from the dentist and spent two hours shopping for health foods in the local alternative-medicine store. Now he's sitting in his Los Angeles home, staring at his shoelaces.

"At some point, you just become aware of the ultimate cosmic truth that all this time your shoelaces have been tied together, you schmuck, and that everything would have been so much easier if they weren't," he blurts in stops and starts, too fast for a court stenographer to follow. "Then you finally untie the laces. You never realized that doing something so simple and technical as that - to just suit up and show up like the other schmucks. Now, to see what most of my peers have been experiencing for the last fifteen years, I've become almost entirely optimistic."

Which very nearly sums up how the actor's skeptical admirers must feel: almost optimistic, entirely.

Well, here we go again. Only, Downey's latest role, as a two-bit New York thief who stumbles into a Hollywood noir, isn't just a comeback from tabloid infamy; the antic Kiss Kiss, Bang Bang, by Lethal Weapon screenwriter Shane Black, fits his darkly comic, hyperverbal talents better than any of his films so far. Even its bleakest, not-for-everyone jokes (one involving a corpse, another in which Downey's character murders a man) throb with the charm, gallows wit, and, most of all, the cynical self-consciousness that are Downey's trademarks, on- and offscreen. He's never been better, or, it seems, more himself.

"You don't have to look too far for parallels," Downey admits. "He's really this post-Gen-X dummy, hell-bent on figuring out one thing in the maelstrom of things he doesn't really understand - who escapes from New York, almost gets himself killed, and in the end, might have a shot at a cool girl."

In 2004, Downey released an oddly mellow album of standards and confessional ballads, on which he dubbed himself The Futurist. But he's always been more of a Cubist. Quick-witted and restless, he circles conversations and characters from a dizzying array of angles. "He has this ability to accommodate tonal shifts - heavy, funny - impossibly seamlessly," says Black. "He’ll lapse into tears, say it's clichéd, then start over again that same second. His mind clicks and clicks. When your brain works that fast - it must be a blessing and a curse."

The blessing is what that hyperkinetic Cubism allows him to do in Kiss Kiss. And the curse is that Downey so often turns that quicksilver, endlessly looping wit back on himself. ("He’s a tortured genius," says Black. "He’s not just some guy with problems.") Ask Downey a question, you don't get one answer, you get twenty - it's practically jazz psychoanalysis. Ask him about the obvious - the comeback, the drugs - and he's off, spilling punch lines and laments, yeses and nos and maybes like marbles rattling out of his mouth.

"There's all those guys that got those action movies I was never cast in and now half of them own half of Idaho," he says flatly. "And some people are not required to have their shit together at all. Do the right thing and you'll get far in this twisted industry?" Downey groans. "I could mention half a dozen people who're really in the fucking barrel. What's that new stuff - Oxy. What's it called?" Downey cheekily asks his assistant, who tells him - "Yeah, Oxycotton. I mean, OxyContin... Me? I need to keep the plug in the jug."

Still, Downey is pragmatic about his situation. "I love it when I see in the paper who's made a complete jack-off of themselves - it amuses me," he says. "So I get it, but at some point at the end of the nineties, studios and insurance companies suddenly started using your private persona to get you a sobriety coach and five hours of fucking Gestalt therapy a week - or we don't pay you."

Now that the insurance companies have cleared Downey to play, Downey has a full dance card for the first time in years. He's in George Clooney's Good Night, and Good Luck; he's wrapped Richard Linklater's A Scanner Darkly; Disney's Shaggy Dog; and the Diane Arbus biopic Fur. Currently, he's in talks to play Edgar Allan Poe in Sylvester Stallone's biopic Poe, and is shooting David Fincher's upcoming thriller Zodiac.

"While not such a flagrant fiend as myself," Downey says of his Zodiac character, "he does find himself hot on the trail of the killer story while he's getting hammered and snorting coke."

And, yes, there's painkillers in Kiss Kiss and opium-smoking in Poe, but Downey swears, "It's not like people say, 'He's the right guy for the job because isn't this life imitating art and I wonder if he'll survive it?' There's no glory in that Stanford Meisner technique, that sleeping-in-the-coffin-isn't-it-fantastic-he-almost-expired-in-his-pursuit-of-truth-as-an-actor...”

He takes a breath, finally.

"These days," he says, "I'm all for aesthetic distance."