Why exactly is Citizen Kane widely regarded as the greatest film of all time?

Well, any decent film requires multiple viewings to grasp the full extent of its message and content. Citizen Kane is certainly no different. It is considered the greaest film of all time in most circles because it is the most ahead of its time film ever made. i mean, it was made in 1940 but the film made use of extraordinary shots and camera movies that are staples today. The cinematography was revolutionary. No one had explored depth of field like welles did in Kane, and it has been replicated only a few times since. The contrast too, was something that had not been explored yet in american cinema. Then there is the content. Kane is essentially an allegory for the life of William Randolph Hearst, who vehemently attempted to defame Welles and kept him from earning his best picture oscar. all in all, the whole back story behind it and the technical achievements Welles mustered were what made Citizen Kane a landmark film in its day, and the fact that the formula it established hasnt yet been improved upon is why it is the greatest movie ever.