I finally went and saw this today. It's perfect. It lived up to all of my expectations and then some.

This movie*so closely skirts the edge of being pure camp that it so easily could have gone horribly wrong in the hands of less capable actors or an unskilled director, but everyone was perfectly on point. Natalie is usually a bit hit or miss for me, but she really turned in a fantastic performance. Her portrayal of madness comes off convincingly, and I was particularly impressed by her performance in the final 30 or so minutes of the film and her ability to showcase the complete transformation of her character.
And a big round of applause for Mila, as well. It might not be inherently challenging for most actresses to portray the "bad girl", but she did so very well. Her Golden Globe nom is much deserved.