Sorry, wasn't sure where to put this. For me:
At the Gates - Slaughter of the Soul. Blut Aus Nerd and I were discussing this in a different thread. The Red in the Sky is Ours is fantastic, but I have never understood the mass appeal of this album.
Bathory - Hammerheart. I love the first four Bathory albums, and I understand that this one was massively influential, but I've never liked it.