Cass is so fun as a character because she fulfils the 'gruff but with a heart of gold' trope in a way that normally is exclusively used for male characters. Cass can be abrasive, and asocial, and off-putting. She is better than everyone, knows it, and she is not afraid to say it loudly to your face. She tried to help Babs feel better after seeing her cry, and decided the best way was to simply throw Nightwing out of a window (it's okay, he was fine).
But Cass is also someone who loves deeply and cares so much. About everyone. She has strong moral convictions to never kill not because she's scared it would push her over the edge but because she values people's lives so much. Because she believes everyone can choose to be better, and they deserve the chance to make that choice.
She isn't sweet and friendly and someone who always manages to get on with people, but she also isn't a cold ruthless assassin. She is a tough, broken person who finds something to protect in everyone. Someone who can frankly be a jerk (and can be difficult for some people to get along with) but who would risk her life time and time again if it meant helping someone. Cass is a hero through and through.
Anyway, I just love Cass.