Sound — 10
This is easily in my top 3 albums of all time. Don't Break the Oath is a timeless classic that will resonate throughout the centuries and show people the very best classic metal band at the very top of their game. It wouldn't be ridiculous to suggest that Mercyful Fate killed traditional metal by laying waste to everything that came before it and all traditional metal that came after it. Nothing equals this. While people's favourites from this album tend to be A Dangerous Meeting and Gypsy, as mine were on first listen, as you get deeper and deeper into this album you begin to appreciate more the savage sinisterness of Desecration of Souls, the epic, fist-pumping, neck-breaking the Oath or the equally amazing closing track, Come to the Sabbath. Other highlights include every single other track. There is no down point to this album, no reason for me to subtract one point. It is traditional metal perfection.
Lyrics — 10
The aspect of Mercyful Fate that lets most people down is the vocals. King Diamond goes higher than just about anyone I've ever heard other than Lust and Urfaust, and most people don't like it. You know that part in Deep Purple - Child in Time where he wails as high as he can? King Diamond is higher than that - for the entirety of the album. At times he sings at a more 'normal' pitch. His vocals are amazing though and you need to listen to this as loud as possible to fully appreciate it. Mercyful Fate use multiple vocal tracks and the vocals become another instrument. Mercyful Fate would not be the same without King Diamond.
Overall Impression — 10
Overall this is simply an unmissable classic. Whether you like black metal, death metal, thrash metal, speed metal, power metal, doom metal or pornocyberscumgrind, you need to hear this. I'd have the Oath played on repeat at my funeral for 6 hours and then put Come to the Sabbath on repeat for the next 6. If you don't like Don't Break the Oath then you don't like metal: it's that simple.