On the one hand, Dark Willow was a bit of a rehash of Angelus--not in terms of character, but in terms of the idea of a protagonist suddenly becoming an antagonist and becoming the new Big Bad. On the other hand, strictly looking at character, Dark Willow added a new dimension to Non-Dark Willow. "Normal" Willow became much less comfortable around her friends after that, and in Season Eight much more evasive when talking about her activities away from Buffy and the rest of the gang. I, for one (and probably others) am much more suspicious of everything Willow now says and does, simply because she could become Dark Willow again (and did, at least in one future/alternate reality in "Time of Your Life" in Season Eight). In Season Six, I thought it was very interesting what Dark Willow said when insulting the rest of the Scoobies. Were these things that Willow thought, or was the dark magic speaking through her? Probably a bit of both, but of course Willow wouldn't admit to that. I agree that the "magic addiction" narrative thread could have been handled better, though I think that Willow still would have become Dark Willow. I'll talk more about that in the other thread, though. I would have liked to see Willow be a bit more repentant for killing Warren, even though she was mostly "not in control" because of the dark magic that overwhelmed her mind, body and soul. She's a bit repentant in Season 7, but seems to have forgiven herself by Season 8. I find it hard to believe that it took less than two years for Willow to forgive herself for killing him, and Buffy and most everyone else seems to feel the same way.