Heavy metal entered 1988 at full commercial strength, but its most important artists were not standing still. Thrash bands expanded their arrangements, progressive metal delivered a landmark concept album, death metal evolved rapidly and European power metal reached a melodic peak. The year’s best records showed how far metal could stretch without breaking its connection to powerful riffs.

Metallica’s …And Justice for All introduced Jason Newsted on bass and pushed the band toward its most complex songwriting. “Blackened,” the title track and “Harvester of Sorrow” used shifting time signatures and long structures to explore environmental destruction, political corruption and war. “One” became Metallica’s first music video, combining the song with images from Johnny Got His Gun. Its growing success carried the band toward arenas, although the album’s nearly inaudible bass would remain one of metal’s most debated production decisions.

Queensrÿche created an even more unified statement with Operation: Mindcrime. The story of Nikki, a disillusioned addict manipulated into political assassination, unfolded through recurring characters, sound effects and tightly connected songs. Geoff Tate’s performance and the twin guitars of Chris DeGarmo and Michael Wilton turned “Revolution Calling,” “Speak,” “Eyes of a Stranger” and “Suite Sister Mary” into a progressive-metal landmark.

Iron Maiden returned to a full concept on Seventh Son of a Seventh Son. The synthesizers introduced on Somewhere in Time now supported a darker supernatural story, while “Moonchild,” “Infinite Dreams,” “The Evil That Men Do” and the title track balanced accessibility with ambition. Helloween completed its own defining story with Keeper of the Seven Keys: Part II. “Eagle Fly Free,” “Dr. Stein,” “I Want Out” and the epic title track made the album a foundation of European power metal.

Thrash continued to branch outward. Slayer deliberately slowed portions of South of Heaven, creating menace through space and control rather than constant speed. Testament’s The New Order refined the band’s melodic Bay Area attack, while Megadeth’s raw So Far, So Good… So What! introduced “In My Darkest Hour.” Germany’s Destruction became more technical on Release from Agony, and Overkill delivered another muscular East Coast record with Under the Influence.

The extreme and progressive underground also made enormous advances. Death’s Leprosy gave Chuck Schuldiner a stronger lineup and production, turning “Pull the Plug” and the title track into death-metal standards. Voivod’s Dimension Hatröss created a dissonant science-fiction world unlike any other thrash album. Outside this Top 10, Suicidal Tendencies fused thrash, punk and melody on How Will I Laugh Tomorrow When I Can’t Even Smile Today, while Ozzy Osbourne introduced guitarist Zakk Wylde on No Rest for the Wicked. By year’s end, metal was not one genre but an expanding universe.