I don't really like this genre. Opeth and Amon Amarth are not melodic death doom. Swallow The Sun and Novembers Doom is all I'll do really as far as what I consider within the parameters of melodic death doom. Go for more pure doom stuff, or pure death for that matter. My Dying Bride and Katatonia are generally solid, check out Draconian and Lethian Dreams too that seems your type of deal and they both do it well. I prefer old school doom/sludge doom/funeral doom/the crustier side of doom, not as polished or cinematic or orchestral or romantic or whatever as those bands and Paradise Lost, Anathema, etc. Bouville can help you with those sissy doom bands, as for me I say go for some real doom like Corrupted, Asunder, Grief, and the like
Clearly you are looking for something else though. Lots of good blackened doom stuff out there too, stuff like Mourning Dawn, Elysian Blaze, etc. It's broad.