I am not disappointed. I recently watched several American movies made in the 50's - from different genres- and The Big Heat is the best. I like its complex plot.
Glenn Ford plays Sergeant Dave Bannion, an honest cop among corrupted wolves. The town is ruled by gangster Mike Lagana. The movie begins with a police committed suicide, leaving a note which will uncover the whole scandal. His widow takes the note with the intention to blackmail Lagana. She tells the police that her husband's health was failing, and that was the reason for the suicide. This reason is unfortunately printed on the newspaper, which is read by the late cop's mistress, who takes the trouble to ring Bannion that there was nothing wrong with his health. The next morning, the mistress is found death. Bannion's suspicion on the widow stirs both worlds: the gangster and the police. It gets worse when a car bomb for Bannion kills his wife instead.
Compared to Tony Arzenta (1973) who also gets his wife killed in the same way, Arzenta knows who are responsible for the murder and kills them all; while Bannion searches for the very person(s) responsible. It is not easy for him, because the whole town is scared of Lagana and none dares to talk. Lagana's thug, Vince Stone (Lee Marvin) is even more dangerous than his boss. Bannion finally gets a little hint about the person who had the car bomb planted; and he gets luckier when Stone makes his girlfriend Debby (Gloria Grahame) angry. Debby will tell Bannion all and helps him to finish what he didn't dare to do. I guess in 1953 the level of violence in this movie must be very high, although by today's standard it is nothing.