So far, there have been three legit responses to this thread. If you don't know what death metal is or don't listen to it, why participate?
So... Morbid Angel isn't death metal?
Well, I haven't heard quite a few of the bands listed in this thread, so I won't debate those, but since the thread poster himself said "Also, yes, progressive stuff like Opeth counts, as does melodeath, techdeath... any kind of death metal"
And what the fuck are Bloodbath
and Death, if not death metal?
Sure they are, but Formulas Fatal to the Flesh is widely recognized as one of their weakest albums. A good case could be made for Altars of Madness or (especially) Blessed are the Sick (and Covenant at least wouldn't be an embarassing suggestion), but Formulas... aspires to be mediocre one day, though it hasn't yet reached that lofty plateau.
The thread starter specifically asked for DM albums that we love the most, not the ones that are "widely recognized" as classics. I just happen to like Formulas more than the albums you listed, even though they are extremely good as well. And fighting over opinions is a bit silly anyways.
He asked for the GREATEST albums. Not "albums you bought last week and have played several times."
Greatness, by definition, means something more than "Well, I really like it."