I always just grouped doom metal into one big, generic, genre (redundant.) Bands that incorperate a lot of depression into their music, but also keep that dark/death kinda sound just go into doom metal for me. Draconian are by far nothing amazing, but they do keep you ineteresyed if that' what you're looking for. I love Candlemass though.

Bleak motifs, yes, though they're hardly exclusive to Doom Metal. Depression and melancholy, I have to disagree with, as the lyrical themes of a true Doom band tend to express more of a heightened sense of alarm over ill-natured things to come, in a fashion which would seem to warn the listener of these things to come, rather than depression and despair. Some classic examples..
Black Sabbath - "Black Sabbath". A song warning the listener of the ills of dealing with occult forces.
Pagan Altar - "The Crowman". "Beware the crow that stands alone..."
Trouble - "The Tempter". "Watch for temptation for it is there"
Reverend Bizarre - "Burn In Hell". "You act like a man of mission. But in whom do you believe?"
Solitude Aeturnus - "Only This (and Nothing More)". "We all fear the word extinction, so we bite the hand that feeds"
And the true Doom ideology retained hope for a resolution to the ills they sang about, rather than showing despair and hopelessness, such as Trouble's "Pray For the Dead", Pentagram's "Prayers For an Exit Before the Dead End", Penance's "Starshined", etc.
The mentality really is much different than those displayed by bands like... say.... My Dying Bride, or Deinonychus, or Skepticism or whatever other bands, who tend to use lyrical themes which revolve around such things as Romanticism, nihilism, and existentialism, which would seem to be taken from 80s Gothic Rock acts rather than from classic/true Doom Metal.

I never knew too much about doom metal, and you have enlightened me. Haha, Candlemass was one of the only doom metal bands I knew of, and at the time when I started listening to them I just thought it was heavy/extreme metal. I was just a little tyke and I never really looked into the ideology of things, but it is a very interesting genre.