Page 2 of 3 -- ''They're what I consider avant-garde," Gordon says, ''and God bless 'em for being able to pull it off."

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Also garnering much attention this spring is Queens of the Stone Age's ''Lullabies to Paralyze," and not just because it's singer-guitarist Josh Homme's first QOTSA album without the band's cofounder and bassist Nick Oliveri. Loud and swampy, it's a collection of songs built on dynamic, propulsive soundscapes, not just tried-and-trite radio-friendly hooks.

Earning less attention but no less deserving is Porcupine Tree's textured ''Deadwing," released last month. Led by guitarist-keyboardist Steven Wilson, the band has been putting out albums since 1991 but received some of the best reviews of their career with 2002's ''In Absentia."

Certainly, it doesn't hurt that prog rock (sometimes called art rock) bands deliver pummeling music that's as cathartic as it is challenging. It's great music for the head and for head-banging. At a recent sold-out Boston appearance, . . . And You Will Know Us by the Trail of Dead singer, guitarist, and drummer Jason Reece said of his Austin, Texas-based band, ''We may be pretentious art [expletives], but we like to rock."

Prog rock can trace its beginnings to the 1960s and such classic albums as the Beatles' ''Sgt. Pepper's Lonely Hearts Club Band," and even the Beach Boys' ''Pet Sounds," both of which elevated pop music from mere entertainment into grand art.

''There's a lot of things you can fit into the genre of progressive -- you could call the Beatles, Beach Boys, and Led Zeppelin progressive depending on what tunes you're listening to," Gordon says. ''Most often it's typified by more complex songwriting, integrating world music elements, odd time signatures, and virtuosity."

By the late 1960s, when most rock songs still clocked in at around three minutes, bands such as England's King Crimson, led by Robert Fripp, began experimenting with longer compositions unbound by traditional formats and structures. In 1969, his band released ''In the Court of the Crimson King," which became a Top 40 hit in America.

By the 1970s, such bands as Pink Floyd, Yes, and Genesis were filling arenas, as well as the headphones of fans eager to discern every musical twist and clandestine lyric. Inevitably, prog performances became more preposterous, avant-garde, and occasionally downright silly, such as Jethro Tull's Ian Anderson prancing about performing flute solos.

Soon, John Lydon, the Sex Pistols' Johnny Rotten, was famously sporting a homemade ''I Hate Pink Floyd" T-shirt on the streets of London, and punk's bracing two-minute, three-chord efficiency became an antidote to the prog-rock blahs.

In the excellent documentary ''End of the Century: The Story of the Ramones," there's a clip, epitomizing prog's excesses, of Keith Emerson, keyboardist of Emerson, Lake & Palmer, waist-deep in an intricate Moog synthesizer solo that's both remarkable and insufferable.   Continued...