Celtic Frost's much anticipated 2006 comeback album, Monotheist, is everything you'd expect from the band who managed to attach the term avant-garde to ugly ol' heavy metal.

It's unconventional, unpredictable, challenging to a fault, head-scratchingly weird at times, frequently brilliant, and anything but perfect.

A simplified stylistic description would have it pegged as some sort of modern gothic doom album, but simple descriptions have never really fit the bill with Celtic Frost -- whether relating to their greatest triumphs, To Mega Therion and Into the Pandemonium, or abject disasters, like the infamous Cold Lake.

The inherently complex Monotheist is no different, and the shared weight of the band's hallowed legacy and inevitably tall expectations don't exactly help the album's inauspicious start, either.

Despite an energetic burst of old-school blackened thrash, opener "Progeny" stands out mostly thanks to those recognizable CF qualities: Thomas Gabriel Warrior's muscular rasp, crusty and brutal guitar tone; and the ensuing "Ground" bores down on interminably ponderous riffs and tediously repetitive lyrics ("Oh, God, why have you forsaken me!") just long enough to leave one seriously worried.

Luckily what the trio (currently comprising founding members Warrior and Martin Eric Ain, plus new drummer Franco Sesa) can't quite realize through brute, stultifying force, they ultimately accomplish via subtler means.

A foreboding, instantaneously infectious melody threads its way through even the heaviest portions of "A Dying God Coming into Human Flesh," and haunting female voices duet with Warrior's alternately deadpan and surprisingly fragile, quavering tones over gothic stunners like "Drown in Ashes" (featuring well-placed synthesizers) and the very unusual (even for this album, even for Celtic Frost) "Obscured," where a semi-industrial ambience actually recalls Berlin-era Bowie! Several subsequent tracks carry on suffering from excessively tiresome doom droning, but almost invariably contain that unexpected twist (like the clanging of rusty bells that introduce "Os Abysmi Vel Daath") or clever bridge ("Domain of Decay") to make them special, or at the very least interesting.

And with the ambitious closing triptych comprising the cyclopean vistas and terrifying shrieks of "Totengott," the marriage of harmony and feedback across the 14 minute "Synagoga Satanae," and the elegant symphonic denouement (there, the classical music angle, at last) of "Winter," Celtic Frost's return should satisfy even the biggest cynics with the scope of its imagination and sheer audacity.

Those qualities, as much as great music, have always represented the cornerstone of Frost's unique body of work, and Monotheist -- unrealistic listener expectations or not -- is a more than worthy addition to it.