Overall I found this film good: exceptional acting with disturbing scenes (some essential, some useless) and weak second half. CONTAINS SPOILERS The film is divided in 2 parts. I thought the first half of the Pianist was terrific. We meet Erika Kohut (wonderful Isabelle Huppert), a piano teacher, and get introduced to her world. She is single, struggling to find her space against an over-protective and borderline tyrannic mother. We understand that she has lost or has seldom experienced love as a physical+emotional chemistry: she protects herself by being sharp and offensive to people, releases her sexual tensions in sex-shops, as a voyeur, or in sadistic self-mutilations ... This first half is very clinical and builds an incredible tension in the film, almost unbearable.
Then comes Walter, a young, handsome and outgoing man (played superbly by Benoit Magimel). Though he gets to feel Erika's coldness in the beginning, he seduces her and slowly wreaks Erika's fortress. He loves her deeply but she needs him to fulfil her sadistic desires. Then when she is about to fall for him, he is disgusted by her world and in the end we discover that Erika is unable to love or feel at all (especially since Walter is portrayed as someone impossible not to love). This is the second half of the film, very touching as we see Erika's inability/inexperience to love lead her to self-destruction. This second half seemed less mastered by Haneke, and sometimes had non-credible (ie. too shocking) scenes which paradoxically lessened the drama.
Of course, this is a crude film at least in the French version: you see porn sequences from the sex shop, daring mutilation and sex scenes. The much talked-about fellatio scene between Magimel and Huppert was quite good I thought, and is central to understand Erika's sick relation to love. As to the actors, Huppert is marvelous all through the film, Magimel gets better and better up to perfection, and Girardot (the mother) is excellent.