This movie hits too close to home: a story about a bipolar man trying to retrieve his life. I mention this only as a caveat ... I'm not the most objective observer.
There are many things that Mad World does well. While we can probably assume that the main character, Tung, has some chemical imbalances, they do not explain everything about his life. Society doesn't know how to treat him or to help him, and the "mad world" creates bipolar people, chemistry or not. The film is sympathetic towards Tung without romanticizing his life. But Chun Wong does not spare us the effect Tung has on others. His father (Eric Tsang) takes him in after Tung is released from a mental institution, and he is ill-equipped for the job. He tries, though, and his life is more difficult because of Tung's presence. (The father was absent during much of Tung's life ... he must also take some blame.) For the most part, though, Tung gets the short end of the stick. He has a hard time getting a job (he was a financial analyst), people shun him and make assumptions about him.
The only person who meets Tung on an equal basis is "Fruit", played by Yvan Hok-Man Chan (I may have this wrong, I'm struggling to understand the credits). Fruit is a young boy with an overprotective mother, a nerd who connects with Tung as no one else can.
The film succeeds mainly because Shawn Yue is excellent as Tung. He plays all sides, the depressed Tung and the manic Tung, believably. He is the reason Mad World is at times hard to watch, but he also the main reason to check the film out.