The one thing interesting to me is that Wall is bringing a painter's approach to photography; he carefully stages his photographs as a painter would stage his picture, making up elements to fit his own artistic sensibilities. That differs from most photographers who, while they may arrange minor aspects of the subject, photograph what is in front of their camera as they found it. Wall truly does utilize the camera to paint his canvas, and he decides exactly what will be on that canvas and where.
Contrast that approach to what most photographers do. Sure, we may alter the light, and we use focal length, aperture, and our location to vary aspects of the final image, but the essence of photography is that we capture what is there.
In short, most photography is about recognizing the inherent beauty/artistic value in a scene and capturing it effectively (so that the viewer connects with our vision). Wall's photography is about creating artistic value from whole cloth, and he uses the camera to capture his creation as an alternative to another method such as painting. The difference in approach is, IMO, occasionally effective for Wall but all too often comes across as contrived and artificial... because he doesn't know when to stop adding content. To me, his less successful images lack subtlety.