I'd have to say that after season six, I stopped liking Willow because she had lost so much of what made her, her. The quirky quiet girl, was replaced by this personality that I did not like at all.
About the magic issue. I think that there is bad magic out there, but I also think that it is the way you use it that makes it evil too. Willow was very weak minded, unlike Buffy, so I guess thats why she succumbed to the dark magic like she did...
