One part it seems which has been overlooked in the few reviews I've read is how this image of feminism illustrates China's version of liberation. Cheung plays Ruan as both a feminist in charge of her career, as well as a woman who is in control of her scandalous affair with Lawrence Ng's character. The difference between her and him being that men are understood to have concubines and are forgiven for the indecency, while Maggie's career is ruined (though she never apologizes for it in any way). Traditional roles still trump profession in 1930's China, but the sadness of it all being retold shows a strong Ruan overcoming every possible trap--losing a career over an affair, especially--and maintaining her desires for success.
For Cheung's performance, it never wavered. I was a big fan of hers in "Irma Vep" and she was just a strong in this role playing Ruan. Effortless shifts between emotion ("So, you're showing me your true face," her lover says as she blows smoke in his face obstinately, then switches to a kindly-wife smile--is she practicing her role in the movie, or is that really her?), graceful poise courtesy of the era before slouching was cool, private display of emotion, and elegant role-play as mistress and ex-wife with Tony Leung.
I'd have to know more about the history of Ruan to know if this is an accurate portrayal of her life, but the film-making style of inter-cutting Cheung playing her in the 30's while interviews with Ruan's colleagues from that time as they are interviewed by the director of the movie is a fascinating way to present her history. Is it a bio-pic? Is it a historical fiction? Is it a retrospective? It's all and more.