While A Trip to the Moon was very much about showcasing special effects and the awe inspiring nature of film on the complete fantasy sci-fi side of things, The Great Train Robbery displayed the awe inspiring nature of film to tackle real people, robbers and cowboys. Due to the strange nature of film as a medium the subject was definitely heightened and thus you had larger than life characters who were performing larger than life actions. But it's interesting to see how the subject of people could be altered to be fantastic just as much as the subject of aliens. And I think as a result the content itself is quite shocking in many ways, especially as the fighting itself is very realistic and we see the robbers act very viciously towards the passengers and bystanders.
At one point in the film around 3:20, one of the robbers brutally beats and bludgeons a train operator to death and tosses him off and it's captured as very matter of fact, making the event feel much more brutal as a result. Since all the shots are wide shots as that was what the medium required. There's something to note about the fact that the majority of the scenes were filmed from a static wide-angle and thus the action that occurs on-screen is made to seem far more cold and distant and brutally honest with what is going on as cuts and other angles can't hide the event.
It's interesting to note that as an early film, The Great Train Robbery depicted the story from the perspective of the "bad" guys who later developed into anti-heroes as there was no real interaction with this medium, yet, and the concept of what characters should or shouldn't be hadn't been fully developed so the choice to take the perspective of the villain says something interesting about the inherent nature of filmmaking to cross this line of good and evil and want to depict the story from the perspective of the "bad" guy. These early silent films almost seem like a very honest reflection of the nature of man, unconstrained by the later complexities of the Modern World with Television and Radio.
Overall the film is very taught and suspenseful, and is significant for using several innovative techniques, location shooting, cutting between different storylines running parallel in time, that hadn't been fully developed yet.