Melissa is considered to be the masterpiece in Mercyful Fate's discography, but for my money, Don't Break The Oath takes the cake. It is strong from start to finish, sporting both Mercyful Fate's musical and vocal strengths. The guitar and percussion work is well above average, and the bass provides a great platform and backbone for the rest of the band. King Diamond delivers vocally, and this album is arguably his strongest vocal performance on any album (minus Abigail). Don't Break The Oath is more than worth checking out if you're looking for the origin of black metal (along with Venom), or just looking for a superb album in general.
Following up 1983's monumental "Melissa" record with "Don't Break the Oath", Denmark's MERCYFUL FATE established a place for themselves in evil music history. This album glows with the best witching metal moments ever created. Shermann and Denner's intricate melodies and harmonies set over the King's wailing vocals and sinister falsetto still qualifies as some of the most evil-sounding music you're likely to hear. If you listen closely, you can hear the influences of early 70's bands like CAPTAIN BEYOND in Shermann's playing and the way the songs are structured. Dancing Madly Backwards....to Satan? "Desecration of Souls" has one of the most killer riffs of all time.