It was an incredible play, and the performance was excellent.
Now, it's a movie with Gwyneth Paltrow, Anthony Hopkins, Jake Gyllenhaal, and Hope Davis. It's still good - I'd like to see some Oscar attention for it. Paltrow occasionally gets the math grad student vibe right, but throughout has the somewhat distracted air that the character would have. Davis is a surprisingly good older sister foil. There's a moment where Paltrow is lost in her thoughts and Davis is attentive to her surroundings that grabbed me - with no words, that few seconds of film told me volumes about their two characters.
I think the play was better, but the movie's very good, too.