Anchored by the punishingly intricate thrash sieges “Hangar 18” (about alien invasion cover-ups) and “Holy Wars…The Punishment Due” (about the Troubles in Northern Ireland), Megadeth’s relentless fourth album ushered in ’90s metal in high-class style, converting shred junkies and prog fanatics alike. In galloping attacks like “Five Magics” and “Tornado of Souls,” new guitarist Marty Friedman and new drummer Nick Menza were high-octane virtuosos, raising the instrumental stakes for both Dave Mustaine’s band and the speed metal subgenre as a whole.