I don't hate Mai, but i don't feel like i'm given very much reason to like her, either.
Mai didn't seem to have any issues joining Azula to bring Zuko back to the Fire Nation in chains -- or dead. She never tried to meet Zuko where he was. She dismissed his feelings when he tried to share them, and yelled at him when he tried to explain his reasons for siding with the Avatar against the Fire Nation. I'm not saying Zuko was a perfect, unobjectionable boyfriend, but his failures don't cancel out Mai's. The one good thing she does in the show is stand up to Azula for Zuko, and that comes out of nowhere with no basis in anything she's said or done up to that point.
I've seen versions of Mai in fanfic that i've liked, somewhat, but it's all invention. Canonically, Mai never has an issue with the war. She doesn't ever show any signs of being intimidated by Azula. The dialogue about her parents being repressive is contradicted by what we actually see of her parents. She calls Zuko a traitor and refuses to listen to his reasoning. And then she turns up at the end, ready to restart her relationship with him, and tells him he's not allowed to break up with her. I'm not sure what i'm supposed to like.