Masterpieces.

Fear Factory - Demanufacture

Rammstein - Mutter

Godsmack - Awake

No, your eyes are not deceiving you. I actually believe that.
 
Hmmm..... let's go way back and to a band not really considered metal:

AC/DC - "Back in Black" Its tough to beat that one. Cover to cover, it's heavy, intense and well written though considered "hard rock."



Bryant
 
Here's what I would consider to be the masterpieces in my collection:

At The Gates-Slaughter Of The Soul
Agents Of Oblivion-Agents Of Oblivion
Black Sabbath-Master Of Reality, Heaven And Hell, The Mob Rules, and Dehumaizer (Dehumanizer is a criminally underrated album if you ask me!)
Deadboy And The Elephantmen-S/T
Dio-Holy Diver
Death-Human
Evergrey-Recreation Day
Guns 'n Roses-Appetite For Destruction
Iced Earth-Something Wicked This Way Comes
Iron Maiden-Seventh Son Of A Seventh Son
In Flames-Colony
Lacuna Coil-Comalies
Led Zeppelin- 1, 2, 4, and Physical Graffiti.
Machine Head-Burn My Eyes
Metallica-Master Of Puppets and ...And Justice For All
Megadeth-Rust In Peace
Nevermore-Enemies Of Reality (Production issues aside...)
Obituary-Cause Of Death
Opeth-Orchid, Blackwater Park, and Deliverance.
Ozzy-Blizzard Of Ozz
Overkill-Horrorscope and Killbox 13 (Which by way is my album of the year for 2003!)
Pantera- A Vulgar Display Of Power
Samael-Ceremony Of Opposites and Passage
Sepultura-Chaos A.D.
Slayer-Reign In Blood and Seasons In The Abyss
Testament-The Gathering
Tool-Opiate, Aenima, and Lateralus
Whitesnake-Whitesnake

That is everything in my collection that I would consider to be a masterpiece. Every single one of these albums will never grow old for me, and to me are all masterpieces.