Six years have passed since Green Day captured the heart of teenage America with the teen-angst anthems of Dookie. Songs about masturbation, marijuana, lousy relationships with parents and even lousier relationships with girls tapped into the mind of every junior high school student, to the tune of 10 million copies sold.

Since then, however, Green Day's fans have grown up and the band has as well, causing Dookie's follow up, Insomniac, to flop. But 1997's Nimrod sparked something of a comeback thanks to "Good Riddance (Time of Your Life)," an acoustic, sentimental ballad that became Green Day's biggest hit to date. The song allowed Green Day to cross over into new, maturer territory and got people wondering where the band would go next.

A collection of 12 new "Good Riddances" seemed the likely destination. The guys in Green Day have never been big on innovation (they've been closing shows by setting the drums on fire for three years now) so a rehashing of their big, sappy hit seemed an obvious path to take.

But Green Day's new album, Warning, is a pleasant surprise. Rather than ballads, it's a collection of more hooky, punchy pop-punk gems with a vibe Green Day's never presented before — optimism.

Gone are the angst and anger that colored every Green Day release, replaced by impassioned calls to embrace the present. "I'm thinking about a brand new hope," frontman Billie Joe Armstrong sings on "Macy's Day Parade," "'cause now I know it's all that I've wanted."

The go-it-alone spirit that echoed through prior Green Day albums is still around, but Armstrong no longer sounds like he's headed for a dead end. On "Castaway," he asserts, "I'm going at it alone," before declaring that he's "leaving in the lurch and taking back what's mine."

Likewise, "Minority" finds Armstrong charting his own course, veering from the mainstream to "pledge allegiance to the underworld," where he's confident he's found the right way to live. "I'm marching out of time to my own beat now," he says, "the only way I know."

Acoustic guitars are everywhere on Warning, but rather than jerk tears, as they did on "Good Riddance," they give bouncy songs a warm, lived-in feel, as if Armstrong is strumming them while sitting next to the listener. They fuel the title track and "Macy's Day Parade" and are noticeably present in "Jackass" as well.

But "Jackass" isn't driven solely by an acoustic guitar, as its centerpiece is actually a saxophone solo. Green Day has never used anything but the traditional guitar/bass/drum combo, but Warning is filled with such toys as mandolins, harmonicas and accordions.

Perhaps the best use by the band of a "non-Green Day" instrument is on "Church On Sunday," where a Farfisa organ backs smarter lyrics than Armstrong has ever written before. "I'm not getting any younger as long as you don't get any older," he sings. "I'm not going to state that yesterday never was." The track races along at breakneck speed, building on The Muffs influence that Green Day first trotted out on Nimrod.

"Church On Sunday" is one of the best songs Armstrong has ever written, but it's still not the best on Warning. That distinction belongs to "Waiting," arguably the finest — and easily the most optimistic — song Green Day has ever done.

Stealing the hook directly from Petula Clark's hit, "Downtown," with a lyrical nod as well, Armstrong walks his listeners under "downtown lights, shining on me like a diamond ring under the midnight hour." The track glistens as Armstrong sounds incredibly focused, although is destination is "anything. . .at all."

"It's the dawning of a new era," he sings. "I'm so close I can taste it. I can embrace this feeling on the tip of my tongue." The track builds and builds, with Armstrong sounding more focused and more pressured by the second. He struggles through the chorus to get the words "I am so much closer than I have ever known" out of his mouth, and then explodes, exhorting "wake up!" at the top of his lungs.

The track serves as a powerful wake-up call, and Warning works as one as well. Green Day is no longer preaching to a teenage audience, and its new message — an optimistic call-to-arms — cannot be ignored.