Why should you watch Taxi Driver? If you've already seen it, then you'll already know the answer. Taxi Driver is one of the few films that truly deserve the tag 'masterpiece'.
Robert De Niro is brilliant as Travis Bickle, a Vietnam veteran who takes a job driving taxis at night. The job soon begins to show his bad side, characterised by a hatred of what he sees as the scum ruining the city of New York. Most reviews give away too much of the plot at this point, but I'm not going to do that. This movie is best enjoyed fresh.
Easily Martin Scorsese's best piece of direction, Taxi Driver takes place in a disturbingly familiar urban jungle. It is difficult not to feel empathy with the main character, no matter how far his madness takes him. This is aided by an excellent script from Paul Schrader and a fantastic score by Bernard Herrmann (of Psycho fame).

In a small French town, the local school teacher, Helene (Audran), is courted by her new friend, Popaul (Yanne), the village butcher, whom she met by chance at a wedding. The two have much in common, though she is hesitant to take the relationship beyond friendship due to a previous hurtful experience. Meanwhile, the tranquillity of the town is disturbed by a vicious murder. A body is found in the woods, the police lack any clues as to the perpetrator of the crime and there is no apparent motive for the killing. After discovering a second body, Helene begins to wonder if Popaul is the murderer for whom the police are searching. This is a fine psychological thriller and a compassionate study of sexual frustration.