This is a very good gangster film and moves away from the young and dangerous type. I think that the script is well worked and really like the idea of a good cop turn bad after going undercover. The film is clever and has a distinct style. Although rather lacking in the action department, what action there is link well with the story telling of Daniel Wu's demise. I am increasingly becoming an admirer of Daniel Wu's work (Hit Team, Purple storm, Genxcops) and cop on a mission is perhaps his best performance yet. The other members of the cast put in good performances too, notably Eric Tsang.
Cop on a mission is not as good as the Daniel Wu films mentioned above but is nevertheless well recommended.
8/10