While there has been willful abandon in critics’ focus on the astonishing chin-formance of Keira Knightley, she does a creditable job as Jung's patient-come-paramour. Maybe she should attempt accents more often, as she often sounds stilted with her natural RP tones.
I found David Cronenberg’s film consistently engrossing; Christopher Hampton's screenplay focuses on a fascinating period in the development of psychology and the director has a sure, steady gaze that suits the material well.
The weaker element is probably the relationship between Sabina and Jung; I don't think Cronenberg successfully conveys the passion Jung feels for her, which eventually reignites the affair that he broke off. When Fassbender is overcome with emotion at the prospect of her leaving him to go to Vienna my reaction was to wonder where this came from so suddenly. In contrast, the response of his wife to his behaviour (Sara Gadon) is beautifully and subtly observed.
The real strength of the piece is the other relationship, the one between Freud and Jung. Starting out as as a friendship born of mutual respect, it grows increasingly fractious as Freud refuses to treat Jung as an equal and dismisses his interest in expanding psychoanalysis into the realm of the supernatural. This facet of Jung's study is given just the right weight, so it doesn't over-balance the main focus (there is a particularly strong – famous - scene where Jung attributes precognition and synchronicity to noises emanating from a bookcase, only to be met with mystified disbelief from Freud).
Fassbender and Mortensen are as good as you'd expect, and there is much better chemistry between them than between Fassbender and Knightley. Cronenberg reveals both men's flaws in shrewd, precise fashion; Freud's reactions to Jung's lack of insight into the limitations placed on Jews and his unspoken sense of belittling at Jung's wealth by marriage (it's interesting that the scene spelling the split between the two follows Jung heading off to a first class cabin while Freud is left to slum it). Jung meanwhile, encouraged by Otto Gross (Vincent Cassell, perfectly cast as a libertine doctor who says no to any form of repression), yields to unprofessional behaviour and undermines his integrity further by lying to Freud about it. There is a fine score from Cronenberg regular Howard Shore, which supports rather than intrudes on the drama. Fassbender should make a sequel where Jung treats his character from Shame.