For now, I'll go with:
Blackwater Park
Ghost Reveries
My Arms, Your Hearse
Watershed
Still Life
Morningrise
Deliverance
Damnation
Orchid
For me, Watershed can't touch BWP or GR, which I truly found to be their atmospherically richest and darkest albums to date. the former being utterly flawless. Ghost Reveries is not without its flaws but I find it very aesthetically appealing. Still Life follows next as far as atmosphere is concerned, though I find MAYH to be much more listenable, so it rates higher. I've found Still Life to be quite difficult to get into, so I'm not sure whether I prefer Watershed to it or not, but I'm enjoying that more at the moment, so it currently rates higher.
I have a feeling I'm in somewhat of a minority!