Citizen Kane shows mastery of film technique because through the use and innovation of filmic devices Citizen Kane is one of the great movies of all time. .
The first shot begins in Xanadu and we see the camera panning up to the words "No Trespassing." Immediately we find that the film is about isolating oneself (kane) from the world. Panning up to this shot, through the bars, and into the sky, conveys a sense of imprisonement and reaching out to the open space of humanity. .
In the news reel, Orsen Wells and Greg Toland actually dragged the film along sandpaper to make it scratchier, more old fassioned. .
Wells also imployed the technique of deep focus in which both the foreground and the background are in focus. A brilliant use of deep focus is when Kane, as a child, is jumping around in the background of his parents talking about his removal from home. Kane is framed here by the window conveying a sense of entrapment. Indeed, this is the thesis of the film: Kane is trapped in childhood. .
Wells and Toland dug holes in the floor in order to create extreme low angle shots. The extreme low angle shots after Kane's political campaign suggest the end of the once heroic Kane and his men. We also see the bashing heads of Kane and his friend for the first time, and it really does feel like giants bashing heads. .
All of these examples and more make Citizen Kane qualify as one of the great movies of all time.