The two-year long-wait is over, and those Mastodon fans encouraged but leery of the slicker production of Leviathan over Remission will be even more bemused, or downright bewildered, by Blood Mountain, the band's first foray into major-label territory since signing with Warner Brothers' Reprise imprint (after all, this was the label conceded to Frank Sinatra as his own when he threatened to leave it).

Blood Mountain is everything fans both hoped for and feared.

Mastodon has dug even deeper in its foray into prog metal, but without losing an ounce of their power, literacy, or willingness to indulge in hardcore punk, doom, and death metal.

Like Leviathan, Blood Mountain is both melodic and downright raging in places.

Matt Bayles is in the producer's chair once more and he's encouraged this Georgia quartet -- Bränn Dailor (drums), Brent Hinds (guitar and vocals), Bill Kelliher (guitar and vocals), and Troy Sanders (bass and vocals) -- to take it to the limit.

And they have.

Blood Mountain indulges and goes deep into the territory of prog metal beats and quests and spiritual revelations that have less to do with Tolkein-ism and more to do with Conan-ism.

There are utterly beautiful melodic passages woven into the heaviness that are reminiscent of Thin Lizzy's dual guitar lyricism -- and the band has confessed to digging Phil Lynott and company.

The vocals -- with guest spots from Neurosis' Scott Kelly, the Mars Volta's Cedric Bixler-Zavala, and Queens of the Stone Age's Josh Homme -- are mixed way upfront and the number of sheer stylistic changes is dizzying.

No, Mastodon should not lose their street cred over this.

For every old fan alienated, a new one will step into the gap and there will be throngs of new ones, more than likely.

Why? Simply because this band does the technical thing as well or better than Meshuggah without sacrificing a bit of the black blood which courses through their veins toward their dark thrash metal hearts.

The set opens with the completely in-the-red thrashcore metal of "The Wolf Is Loose," complete with a chanted chorus.

As the guitars twin and scream, bass and drums chop away at convention.

Tempo changes, from fast to faster to a refrain that gives the listener time to shout along.

The doubled leads and repetition in the verse are countered by the swelling, pulsating thud from the drum kit.

Lyrically, it appears that Mastodon is trying to create a new mythological present.

But the bridge goes into the netherworld with actual sung vocals and angular, elliptical phrases that defy elucidation.

The echoey sound effects on the drums at the opening of "Crystal Skull" quickly give way to a plodding power metal riff.

"Sleeping Giant" comes out of the gate, slowly, dreamily, seductively, there are digital delays on the guitars that gather tension as they (relatively) whisper by, and create an ambience that crosses early Black Sabbath and Opeth.

It's the vocals that are most remarkable, however, sung cleanly to a slow tempo, each word is distinct and the effect is nearly hypnotic as the strange, self-created cultic myth is further woven into a web of dislocation, epic ambivalence, mystery, and power.

Prog metal is made plain on "Capillarian Quest," where intricate patterns and bludgeoning guitar riffs vie for dominance but are authoritatively held in Mastodon's deafening balance.

"Circle Cysquatch," with its bloodcurdling extreme thrash and burn, tips it toward a virtual creation idea born of pagan rites, blood sacrifice, the spirits of extinct species, and the hollow ring of organized religion, all given their freedom here to drift back to prehistory and the days of fire and rage in the rough and tumble founding of "civilization."

On it goes.

Mastodon seeks no easy answers but poses dozens of questions about origin, and "culture." Forget "thinking man's metal," this is metal, period, and the guys that make it think.

The music, as varied and tumultuous and, in places utterly beautiful as it is, place the band beyond the pale -- check the intro to "Bladecatcher" before it falls apart into pure chaos and cacophony where lyrics and themes are barely articulated in the hammering thunder of apocalyptic noise.

Sound effects that perhaps are the voices of the spirits themselves make themselves heard in the din -- but indecipherably.

"Colony of Birchmen" and "Hunters of the Sky" are both prototypically metal and act as the album's hinge pieces, where Mastodon completes its achievement and establish a new heavy metal.

"This Mortal Soul," with its elongated beginning and utter lyricism may alienate those who live for heaviness alone, but it will attract those who can see outside the genre's subgenres.

The set closes with "Pendulous Skin," a track that amounts to a densely populated power ballad with gorgeous guitar soloing, and a major/minor key chord progression (instead of riffs and a Hammond B-3) played by Bayles followed by a long silence, where at the very end, a "fan" letter is read and responded to.

What does it add up to? Something old and something new, a heavy metal that's utterly gargantuan to wrestle with because it actually moves the style into brand new territory, an unfamiliar terrain which will accord it much name calling and crying of "sellout" by the unwashed masses who are more conservative about their steely brand of "folk music" than the Newport crowd was about Dylan going electric.

Yet, for those daring enough to take this in, there are true bloody treasures to behold and receive.

If Leviathan was a masterpiece, then this is too -- only more so.