What, in Your View, Are the Key Elements of the Third Man That Accounts for Its Success and Durability?

What, in your view, are the key elements of The Third Man that accounts for its success and Durability?
The Third Man is a timeless classic; set in post-war Vienna about an American uncovers a ruthless mystery. The film is still a success today, 61 years later. The mysterious nature of the film and the way Holly uncovers the truth is one aspect that accounts for its success and Durability. Another is the characters and the way they are portrayed. The unusual actors were also a success. In addition, the way the film was shot and the camera techniques used are second to none. All these aspects were used to great extent to create a timeless film noir text.  
The Third Man is a classic Film noir text with a tinge of thriller, throughout the film the element of surprise; mystery and wrong first impressions are shown continuously. This contributes to the success the film was and still is today. Film Noir, with its tempting women, black-market, dark scenes and above all mysterious nature, appeals to the general public. Not only does The Third Man have these film noir elements, but it the confusing plot makes the audience think. The film is not direct in telling the audience what is happening, as it is full of hidden hints and meanings. Examples of Carol Reed the director’s indirectness are: when Harry nods to tell Holly to shoot; when the cat sits at Harry’s feet to indicate it is Harry; the meeting of four people and when the teddies are shown in the place of the children dying. As the film is such a mysterious one, the audience has to use all their senses to understand the plot. For instance: hearing Holly shoot Harry; Harry finds out he is surrendered in the sewers by hearing voices and seeing the shadows throughout the film to indicate who is hiding. The language difference leaves English speaking people slightly naive to what is going on. This makes the audience empathise with Holly as he is in the same situation and leaves the audience guessing. Also it makes the...