Five years after attaining the holy grail of critical and mass appeal with their surprisingly ambitious concept album "American Idiot," once-hopeless punks Green Day [ tickets ] pull out all the stops to one-up themselves with "21st Century Breakdown"--another rock opera.

On paper, it seems like a recipe for disaster. But, in truth, the band's unfailing instincts for writing tight pop riffs and strong melodies serve to inoculate it against the bloat that tends to sink such projects.

Like "American Idiot," "21st Century Breakdown" follows two characters--one who's impulsive, the other more introspective. The narrative is so loose (or impenetrable) as to barely exist, but generally describes a couple negotiating its way through the ruins of the George W. Bush administration.

As you'd expect from the genre, there are plenty of ballads, strings and piano interludes, but Green Day has held onto enough of its punk roots to keep the proceedings from getting overly grandiose. Just one song clocks in over the five minute mark, and that track ("21 Guns") is a ballad deserving of its length. The best of the ballads here is "Last Night on Earth," which owes more than a little to John Lennon.

Following The Who's rock-opera handbook, the album has a liberal dose of anthems ("Viva La Gloria," "Murder City" and "East Jesus Nowhere" are the most notable).

The best track of the bunch is "Horseshoes and Hand Grenades," built around a riff familiar to anyone who owns any previous Green Day album. But this one comes across as Green Day on steroids, and perhaps is the one track here where producer Butch Vig--who's wise enough to leave well enough alone--made a mark.

While not a huge step forward, this is a step forward, nonetheless. Green Day is still pushing the edges of its trademark sound on "21st Century Breakdown," and have learned enough from rock history to keep a potentially unwieldy train on the tracks.