The majority of the female characters were killed off on ATS. Many of them were very evil and a few really good ones. Faith did improve after being on ATS. Cordy grew as a character, but then season four destroyed it again. Partly Charisma and part Joss are to blame for that.

Angel is a dick. He hid it on BTVS. On ATS, he would use those who trusted him. He does things that Buffy would not approve of in anyway. She never knew about most of those. Angel made sure of it. He even had her followed so he could keep tabs on her. Not much of an Angel fan. LOL!