Exercising agency is an important part of art: listening to a polyphonic contrapuntal piece of music necessarily involves the active process of the continuous shifting of one's attention from voice to voice. Watching a film is the same way, in that we can engage with the movement of objects in the frame with respect to each other, or with respect to the shifting parallax of the scenery as the camera tracks through it, or in any other way one can think to. Garry's Mod is an aesthetically revolutionary experience with regards to movement as a form of agency. A game is at its best as a cathartic exercising of one's agency within a set of mechanics, and Garry's Mod has exactly one mechanic: as one creates props around yourself, so the world creates props around you. The buttons only control menus, there is no story, or narrative. You do not directly control the world around you, you morph the world in your own image. This had been done before in pc games like Half-Life 2, but the reason Garry's Mod feels so alive is that the camera is positioned in such a way that one isn't constantly reminded of this fact. The game is posited not as a sandbox game about creating a world from nothing, but as a subjective experience of being a physical object that can engage with its world in the most intuitive way imaginable, by the operation of Newtonian physics.