The style Mercyful Fate employed on Don't Break the Oath resembled a mixture of heavy metal with progressive elements, lyrically preoccupied with Satan and the occult and distinguished by King Diamond's theatrical falsetto vocals. Although very influential to future black metal bands due to its lyrical content, the music itself is more reminiscent of traditional heavy metal. The album was remastered and subsequently re-issued on Roadrunner Records in 1997. This reissue came with the bonus track "Death Kiss (Demo)", which would eventually evolve into the album's lead-off track, "A Dangerous Meeting". Metal-Rules.com named this the greatest extreme metal album of all time.