It has been described by many as, apart from the one idea, just a bog-standard horror film. We took it to be a black comedy, at least at the start.
The American girls are ditsy, shallow and obnoxious. They have no clue about anything except having a good time, complain and force everyone to speak American. If you remade it today, you could definitely make this film a Trump commentary.
They do lots of shrieking. There’s almost no actual horror, almost no blood and guts, occasional bad language, slight toplessness and no excrement (real or pretend). There are some weird bits, but people like David Lynch were making arty films with weird bits, and they are minor.
Apparently it’s medically accurate. There aren’t many nutrients in poop as it comes out of the body, so passing through a second into a third person would mean the last would be struggling, as depicted in the film.
There are all sorts of strands that could be investigated. Was the scientist mad? If you had people willing to do this, would you or could you? What does it tell us about the world’s view of American tourists? Why is the man at the front, and why is he Japanese? And so on…
Is it a good film? No. Could it be shown on tv? With warnings, perhaps. Plenty worse have been shown. Will we watch it again, or the sequels? No.