As I said, for the most part she was good, but there were parts when I thought she was trying a little too hard. That main scene that sticks out in my mind is the one in which Charlize and Christina's character are at some diner, and then Charlize blows up at the waiter for telling Christina to stop smoking. I felt that every line delivered in that scene was delivered incorrectly, especially "Bring it." It's mainly just that scene; I was perfectly fine and forgot it was even Charlize for most of the film. I felt Naomi did a better job, as her performance really gripped me, had me at a near emotional breakdown for a good part of the film.
And besides, me saying anyone overacts IS an opinion just as me saying Lost in Translation is the best picture of the year. It's all relative.
But again I say she overall performed very well, just not amazingly as most people hype her to be. I think all this hype she's been receiving is due mostly to her uglification, and I think that's a shitty thing. There were better performances this year--that's all I mean to say.