It seems that you're bringing to question not the quality of acting but rather a judgement on character. You like Mrs. Mills' character better than Grace for various reasons which you voiced out in your plot descriptions. You say anyone could play a "mad" character. Yeah, anyone could play a mad character. Have the actor who played Mrs. Mills' play Nicole Kidman's part (Grace) and the movie would've stunk. If you mean to say that Nicole Kidman didn't do a good job acting out her part, then I disagree with you. She not only did a good job with her part but she brought charm to the movie that otherwise WOULD NOT have been there without her. And if anything else, having a cameo name like Nicole Kidman in any movie gives the movie "perceived value"--we don't think about it, but it's true. If Brad Pitt is in a movie, even if a movie stinks so bad, we still give "revere" it as a movie because Brad Pitt is in it. Whereas, if Joe Somebody was in it, it wouldn't even be in the big screen: "movie? what movie?" That's showbiz for you.