Quality production, costume, and delivery. Poor writing.
The lead role's character developed quite slowly. The writers tried so hard to make her look ungrateful and reckless but failed due to illogical experiences they used. Ava killed a demon in the first episode at the church, then killed the nun at the orphanage and didn't feel anything. In trying to make a character that secretly fights for humanity, you don't make them kill in the first two seasons. Especially killing a human being (since her heroism is killing demons).
She, falling for that scam of a boy and him dumping his friends for her shows poor conceptualization of bad decision making.