Although rooted in the thrash metal genre, the album showcased the band's musical growth and lyrical sophistication. Bassist Cliff Burton introduced the basics of music theory to the band and had more input in the songwriting. Beyond the fast tempos of its debut Kill 'Em All, Metallica broadened its approach by employing acoustic guitars, extended instrumentals, and more complex harmonies. The overall recording costs were paid by Metallica's European label Music for Nations because Megaforce was unable to cover it. It is the last album to feature songwriting contributions from former lead guitarist Dave Mustaine, and the first to feature contributions from successor Kirk Hammett.
Although rooted in the thrash me,tal genre, the album showcased the band's musical growth and lyrical sophistication. Bassist Cliff Burton introduced the basics of music theory to the band and had more input in the songwriting. Beyond the fast tempos of its debut Kill 'Em All, Metallica broadened its approach by employing acoustic guitars, extended instrumentals and more complex harmonies. The overall recording costs were paid by Metallica's European label Music for Nations because Megaforce was unable to cover it. It is the last album to feature songwriting contributions from former lead guitarist Dave Mustaine, and the first to feature contributions from successor Kirk Hammett.