This is a little different, I have in my spare time put together a personal list of Metal albums that I felt gave a good taste of different styles and changes over the years. It's never done, and I couldn't make it a top 20 so as of today...
1. Black Sabbath – Paranoid (1971)
2. Deep Purple – Machine Head (1972)
3. AC/DC – Back in Black (1980)
4. Motorhead – No Sleep‘til Hammersmith (1981)
5. Ozzy Osbourne – Diary of a Madman (1981)
6. Venom – Black Metal (1982)
7. Iron Maiden – Number of the Beast (1982)
8. Mercyful Fate – Don’t Break the Oath (1984)
9. Judas Priest – Defenders of the Faith (1984)
10. S.O.D – Speak English or Die (1985)
11. Slayer – Reign in Blood (1986)
12. Metallica – Master of Puppets (1986)
13. Guns and Roses – Appetite for Destruction (1987)
14. Suicidal Tendencies – How will I laugh tomorrow…(1988)
15. Morbid Angel – Altars of Madness (1989)
16. Godflesh – Street Cleaner (1990)
17. Death Angel – Act III (1990)
18. Soundgarden – Badmotorfinger (1991)
19. White Zombie – La Sexorcisto: Devil Music, Vol. 1 (1992)
20. Pantera – Vulgar Display of Power (1992)
21. Carcass – Heartwork (1996)
22. Marilyn Manson – Antichrist Superstar (1996)
23. Type O Negative – October Rust (1996)
24. Rage Against the Machine – Battle of Los Angeles (1999)
25. Rammstein – Mutter (2001)