"Kill 'Em All" features intricate riffing reminiscent of the NWOBHM bands played at high velocity. The album is considered crucial in thrash metal’s genesis because it introduced fast percussion, low-register chords, and shredding leads to the genre. Hammett played some pentatonic patterns in addition to his breakneck solos. Ulrich adopted a double time snare pattern that would become a mainstay on Metallica's subsequent albums. Hetfield's vocals evolved from the melodic wail on "No Life 'til Leather" to a rough-edged bark, and the entire band played faster and more accurately on "Kill 'Em All". Author Joel McIver described Burton's and Hetfield's performances as nearly virtuosic, highlighting Burton's smooth-sounding bass and Hetfield's precise picking skills. According to journalist Chuck Eddy, the juvenile lyrical approach to topics such as warfare, violence and life on the road gives the album a "naive charm". The musical approach on "Kill 'Em All" was in contrast to the glam metal bands who dominated the charts in the early 1980s. Because of its rebellious nature and Metallica's street appearance, it appealed to fans who were not into the mainstream of hard rock.