To say that Iron Maiden's The Book of Souls was ardently anticipated would be a vast understatement.

Though it was (mostly) finished in 2014, vocalist Bruce Dickinson's cancer diagnosis and treatment delayed its release until he was medically cleared.

While 2006's A Matter of Life and Death and 2010's The Final Frontier showcased longer songs, Book of Souls is epic by comparison.

Their first double album, it's 92 minutes long, and three of its 11 tracks are over ten minutes.

Steve Harris contributed one solo composition, and co-wrote six tracks with various bandmates.

Dickinson -- for the first time since Powerslave -- wrote two solo tunes, the album's bookends, and collaborated on two more.

The music is cleanly divided between the two discs.

The first is tight; it offers a bit of everything that makes Iron Maiden...well, Iron Maiden.

It is seemingly self-contained.

Dickinson's "If Eternity Should Fail" is an impressive showcase for his voice.

Its dark intro and atmospherics are eventually transformed into one of the heaviest tunes Maiden's recorded in a dig's age, but he climbs above the sonic mass.

"Speed of Light" is a burner.

Dickinson's fury is accompanied by a rockarolla riff, soaring metal guitar fills, and Nicko McBrain's grooving drums.

Harris' 13-minute "The Red and the Black" has a martial tempo and chant that recalls "Rime Of The Ancient Mariner." It's followed by "When the River Runs Deep," a chugging hard rocker with all three guitarists challenging one another.

The title cut is theatrical, as acoustic guitar and a sparse synth are filled out with a knotty riff and solo breaks, emerging as a slower, heavier headbanger.

By contrast, disc two is structured almost narratively; it slowly enlarges and expands to serve an unexpected conclusion.

Opener "Death or Glory" is another crowd-catcher as Dickinson soars above thudding drums and guitar choruses redolent of Thin Lizzy.

"Shadows of the Valley" is the only clunker.

It's dull and predictable, a minor distraction that doesn't measure up to the set's ambition.

"Tears of a Clown," written by Harris and Dave Murray, is for Robin Williams.

It's a clamorous rocker, yet the lyrics and melody are simultaneously empathic and disconsolate.

"The Man of Sorrows" follows expertly, progressing from meandering ballad to theatrical hard rock.

Dickinson's 18-minute "Empire of the Clouds" is about the R101 airship disaster of 1930.

It's Maiden's longest song, but a grand conclusion.

He plays majestic classical piano throughout, as tasteful, biting guitars create a complementary melodic labyrinth amid swelling orchestral strings.

They add texture while McBrain's swinging drums add drama.

It's a heavy metal suite, unlike anything in their catalog.

Producer Kevin Shirley does a stellar job capturing an "in studio" sound that allows for spacious dynamics and warmth without artifical mass.

Who would have thought that after decades Iron Maiden would have an album as fine (let alone as long) as The Book of Souls in them? With repeated listening it earns shelf space with their finest records.