Lau Ching Wan did not receive an Oscar nomination for portraying Inspector Chan Kwai Bun in Mad Detective.
Lau Ching Wan plays that central character who we first meet as he pulls a Vincent van Gogh and cuts off his own ear to give to his boss as a retirement gift. This leads the Inspector to be fired from the force because it is rather obvious that he is a schizophrenic. Lau Ching Wan's performance is all about creating the state of the mad detective since he's always mad whenever we see him on screen. There is never a point in which he seems "sane" so to speak since even his most sane conversations are with his wife, who just happens to be only in his head as well. The mad detective's abilities as a detective come from his ability to be able to see the different personalities that influence people to cause crimes. No one else can see these people though and it is seen simply as hallucinations by others. As a performance as at least an assumed schizophrenic Ching Wan's performance is a bit unique because unlike say Jake Gyllenhaal in Donnie Darko or Russell Crowe in A Beautiful Mind where those actors both portrayed the pain inflicted upon them due to their condition, Ching Wan portrays Inspector Bun to be a man who wholly embraces his insanity.
Ching Wan goes head first with his performance since he is always within whatever realm of thinking that the mad detective is in. Ching Wan portrays Bun as though he is always watching and observing everything around him, as though he is in detective mode even at the beginning of the film when he spots a shoplifter being prodded by one of their alternative personalities. There is an intensity with this by Ching Wan as he brings a great deal of distress in Bun as he sees these other people. Of course this is no distress for seeing them, but the distress always comes from the inspector's desire to stop the crime, or at least the criminal personality from influencing the person. The moments where Bun is allowed some solace is when he is interacting with his "wife". There is such a earnest warmth and tenderness Ching Wan brings in these interactions as he shows that his mental state can be a comfort for the man. The particularly effective scenes in this regard is when we see it from the real perspective and merely watch Bun interact with an empty space. The love that Ching Wan expresses in Bun's eyes though seems to oddly give that space substance.
The inspector is called upon a younger detective having trouble with a case and needs the expertise of the mad detective to help him. These bring about what are really the highlights of the film which are when Inspector Bun is truly in his element, which is whenever he is solving a crime with his seemingly superhuman abilities. Ching Wan matches this idea with his performance as he shows absolutely no hesitation in the detectives manner as he goes about his investigations in his own way, which includes reenacting parts of the case himself. Ching Wan is very entertaining actually in these scenes as he plays it as almost a sort of dance as the inspector maneuvers through the crime scenes. Ching Wan realizes the style of the mad Detective quite effectively as he takes us through his odd method of solving the crime. Although the method is indeed mad the way Ching Wan manages to perform it gives an odd credence to it even before we find out whether or not the inspector actually produces any results. There is indeed something compelling though simply through Lau Ching Wan's portrayal of the mad detectives insanity since he manages to create that purpose within every weird action he takes.
The film I feel takes a bit of a wrong turn in that he begins to somewhat ignore the character study of Inspector Chan Kwai Bun within the investigation, and slowly gets too caught up with the other elements of the plot. In this case it is mainly the other police officer they are investigating for the crime begins to attempt to set up Inspector Bun in a way that convinces the younger detective to not only doubt Bun's abilities but also begin to think that it is in fact that Bun is the killer they are looking for. The main problem with this is it takes away time from Lau Ching Wan which is not a good thing, and when it gets caught into the mechanics of the plot it begins to forget that the mad detective is the only character interesting enough to carry the film, the evil cops multiple personalities could have perhaps but they don't quite realize them well enough. The scenes with Inspector Bun though still do stay intriguing, and there is one particularly good scene for Lau Ching Wan when Bun is confronted by his actual wife, while being spoken to by his imaginary wife at the same time. Lau Ching Wan's terrific in the scene by providing the confusion in the detective as it is obvious he does not know quite how to comprehend two things trying to occupy the same space. The film unfortunately decides to end with the least interesting aspect of the film which ends via a rather standard shootout, Ching Wan still gets a memorable moment when he executes the main villain, but his own story feels somewhat ignored. Even with the somewhat underwhelming ending for his character Lau Ching Wan still manages to create quite the fascinating sort of madness with the role, and I only wish the film had more closely focused on this.