Demonic,
I'd like to point out that this is why I love Dragon Age. People have different views on the characters because of the depth surrounding them.
In this we are entirely agreed!
As for AD&D alignments for party members, I think I would go with this:
Alistair: NG. He doesn't do much in the way of impulsive things, but he isn't really into planning, either, preferring to allow others to do the thinking. The 'Goodest' member of the group, though.
Leliana: was LE (Planner, assassin), is trying hard to be NG when you meet her. By the end might be NG or NE depending on your choices.
Sten: LN. Follows the laws of his own people to the absolute. The evil thing he does to land him in the cage is the result of temporary madness and not a part of his usual character.
Morrigan: LE (Yes, the AD&D alignment system is very High Fantasy). Seemingly more interested in her own amusement than anything else, Morrigan nonetheless has a long term plan that is mainly of benefit to herself and can plan on the fly when she has to (As with her personal quest).
Zevran: NE. Zevran is totally amoral and goes where the winds of fate take him. He is not going to protest at very evil acts, nor at very good acts, either, but at the same time he doesn't perform good or evil acts himself unless he feels he has to. Zevran is probably a sociopath in that the only person he actually cares about is himself (Although if befriended or romanced, he will care about what happens to the PC, too). I nearly went with TN for him because he's entirely a reactive character. He's not ever going to do anything unless forced to by other people or by circumstance.
Wynne: LG. Planner, cares about others. I get the impression that Wynne has sort of become LG through slow progression over many years, so she's more lg than LG, if you get me. She's a bit relaxed in both and has certainly done many things in her past that are not really either.
Oghren: CN. Oghren is a creature of impulse, who stumbles from one train wreck situation to the next, usually while drunk or pursuing the next skirt, or both. Hopeless at anything that involves planning, he's simply there to hit things.
Loghain: LE. Master planner who is out to accomplish his own goals come what may and who could not care less who might get hurt by the fallout - including his own daughter! The very definition of LE, in fact.
Duncan: LG. Believes that the greater good trumps all else and is wiling to risk all in order to defeat the evil that threatens his land. By any measure, Duncan is LG.
And the really great thing with DA:O is, as you say Demonic, that every one of those alignments could be debated over with plenty of evidence for and against, because the characters really are that nuanced
