After MasterOLightning
1. Agalloch - Ashes Against the Grain: 11
2. Amorphis - Tales from the Thousand Lakes: 23
3. Bathory - Blood Fire Death: 24
4. Celtic Frost - Morbid Tales: 3
5. Coroner - No More Color: 23
6. Death - Symbolic: 29
7. Dio - Holy Diver: 14
8. Dismember - Like an Ever Flowing Stream: 26
9. Fates Warning - Awaken the Guardian: 24
10. Iced Earth - Burnt Offerings: 4
11. Immortal - At the Heart of Winter: 23
12. Jag Panzer - Ample Destruction: 6
13. Manowar - Hail to England: 16
14. Megadeth - Killing Is My Business...: 22
15. Metal Church - Metal Church: 21
16. Metallica - Kill 'Em All: 34
17. My Dying Bride - Turn Loose the Swans: 29
18. Nokturnal Mortum - The Voice of Steel: 10
19. Rainbow - Rising: 4
20. Venom - Black Metal: 27
Metal Church/Rising/Symbolic
In my opinion, Deep Purple stuff don't belong here. If we add any of their albums, 1,000 other rock bands would fit. This is a metal list.
I don't see how In Rock or Machine Head are any less of metal albums than Paranoid. Speed King, Flight of the Rat, Hard Lovin' Man, and Highway Star, are pretty much as fast and aggressive as metal/rock of the early 70's ever was until Judas Priest took it further, and Pictures of Home, Space Truckin', Into the Fire, and probably others are still plenty heavy. Outside of Black Sabbath I don't think there was any band as metallic from 1970-1975, and even if their albums had an overall slant towards hard rock, there are other songs like Fireball and Burn that did plenty for metal's development as well.
Plus, Metal-Archives says they're metal and they are the ultimate authority on everything.