"Gesamtkunstwerk" is a German term coined in the 19th century. It roughly means "total art." It's actually a term that extends back in time to the development of Italian Opera, particularly in Venice, where commercial opera originated. It refers to the idea that "modern" Opera represents a combination of all of the Classical Arts. I don't have the list handy, but we're talking: architecture, music, song, dance, plastic arts/sculpture, etc. The productions were elaborate. As Opera spread across Europe, this strong classical artistic pedigree was lessened by independent local traditions. In Germany, musical ensembles and singers were independent entities. England had a strong tradition of theater. Thus, the original Operatic vision was transformed and weakened.
The idea of Gesamtkunstwerk was popularized in the 19th century by Richard Wagner. Quoth the Wikipedia, 'Wagner's own ring cycle represent the closest anyone has come to realizing these ideals."
Gesamtkunstwerk was also an explicit inspiration to the Bauhaus movement in architecture, and you can also detect it in the Craftsman movement in the UK and the US.
Events in the 20th century conspired to discredit "total"-isms in the eyes of all. Wagners Gesamtkunstwerk took on a sinister tinge. No longer would Artists attempt to unify all arts in a single endeavor. In fact, the entire idea of classical art was eclipsed by technological developments in the 19th and 20th centuries that created new fields of art.
Specifically, Film created an entirely new category of art that could make the same kind of attempts at achieving Gestamtkunstwerk as Opera. This comparison has been muted by the lack of common vocabulary to discuss the respective art forms: film scholars don't really write about opera, and opera buffs don't write about film. That such a simple comparison could go largely unremarked upon (Specifically, that opera and film have similar relationships with their respective audiences in their attempt to combine art forms in a single project.)
It should be observed that you can't argue that advancing technology makes the possibility of achieving such an impact in a Film is higher, but it is unclear whether Audiences actually want experience Gestamtkunstwerk at all. Certainly, if you look at the films people pay to see, the tone is short of an all encompassing artistic experience. From an asethetics perspective, I would argue that Gestamtkunstwerk is undesirable to most Audiences.