I loved her and hated her at the same time.
I loved her because in a way she wasn't really selfish, but she was very selfish. I mean, she saved Buffy's life BEFORE she went after Warren. I liked that the reason she went evil was because of Tara, it REALLY shows how much she loved her. It was great how she was defeated by Xander simply saying he loves her, and giving the speech about the crayon she broke in kindergarten (which was so sweet... I can just picture that... little Willow holding half a crayon in each hand and crying with little Xander sitting by her having absolutely no idea what to do... typical). Xander messes with people. But in a good way.
I hated her because... uh, because she was evil and veiny and scary and she tried to destroy the world. I wouldn't have hated her if she HAD destroyed the world, but she didn't. She failed. It didn't work out. Plus, I know Willow was in there somewhere, she couldn't have just turned completely evil, obviously, because Xander stopped her at the last minute... but seriously, she could've controlled herself if she really wanted to. I think that it wasn't completely Dark Willow who tried to destroy the world... there is no way she could get like that without Willow helping with some part of it.