Orchid, the most depressing? I believe that everybody's opinions are equal in that we all have the right to them, but not all are equally valid. This isn't quite an example... but I still find it very hard to understand.
First of all, I'd venture a guess and say that Morningrise contains more minutes in acoustic guitar tracks than any other album (and therefore more clean parts). Orchid contains some of their most triumphant moments, in my opinion. See the beginning of In Mist She Was Standing, much of The Twilight Is My Robe, Requiem, much of The Apostle In Triumph.
I would say, for most depressing album, it's a tie between Morningrise and My Arms, Your Hearse. MAYH because of the story and some of the music, Morningrise because of the music and the fuzzy quality the recording has. Still Life (my favorite Opeth album) I don't find to be all that depressing. Though the story is depressing, I find it angry at times, but mostly epic. Blackwater Park, dark. Deliverance, dark and a bit mysterious. Damnation, melancholy.
... Opeth isn't depressing under my standards... go listen to some old or mid era Katatonia, or sad riden doomy bands...
some melancholic moments, but they play way too well to be labeled depressing, their sound is fulfilling.