I find Cersei on the show to be a much more rounded character than she is in the books. The show demonstrates her concern about Joffrey's insanity and gives us moments where we see what marriage to Robert has done to her. She seems to almost, sorta, kinda, care about Sansa as much as she's able. Book-Cersei is much more a one-dimensional villain.

Rational people might see this as a good thing, a way that the show gives depth to a female character who came off as flat in the novels. This person, not so much.