A Chinese friend convinced me to watch this interesting film, as he was a recovering addict like the character in "Quitting." (I understand the title in Chinese translates into "Yesterday," which, upon finishing watching the film, I thought was a much better, more befitting title than "Quitting.")
As other reviews have pointed out, this is based on a true story and played out by the real people who had expererienced the events. I was certainly surprised to learn that even the patients at the mental hospital were real patients, because they did a fine acting job. In any case, Hongsheng's father and mother did a decent job, although in a few scenes their acting is rather stage-like. Hongsheng's sister is one hot Asian girl! I understand she, like her brother and parents, is also an actor; too bad she does not get much screen time at all.
Of course, the focus is on Hongsheng himself, a young actor who got addicted to illicit drugs. The story is about his recovery. The first half is a bit bland as Hongsheng's parents arrive in Beijing to live with him, care for him and lecture on him. The second half, when he strikes his father (oops, spoiler!) which finally turns him around, is excellently scripted and filmed. It's touching yet not pretentious.
The most interesting aspect is probably the father-son relationship depicted in the film, which is totally unlike any I've seen in Asian films. You have to watch this to feel for Hongsheng's parents during the darkest days.
Finally, the dialog is in Chinese but the English caption is better than most. Lately I've developed a taste for indie films, and I rate this highly and recommend to anyone who's interested in this subject.