1. Horror director Eli Roth made this movie as a tribute to the cannibal genre of Italian horror films of the late 1970's and early 1980's.
2. By making this movie rated R, the movie gave up the ability to really go for the guts (so to speak), so it's weak sauce compared to the grindhouse classics that inspired it, like Cannibal Holocaust and Cannibal Ferox (those two films didn't even bother getting a rating, so their violently cruel scenes are still infamous and remarkable, even 40 years later).
3. This movie is about a group of annoying, over-privileged college students who take a trip to Peru to protest the destruction of the Amazon rainforest and the natives that live there. The plane crashes, and the students meet some natives that torture and eat them, I guess because Amazon natives hate all white people.
4. It seems like Roth knew that making a full-on cannibalistic massacre of white people would not be successful, so he tried to justify the violence by stapling it to the end of a different movie about saving the rainforest. This way, Roth is apparently trying to use the movie to make a satirical statement about social activism or the inescapable cruelty of the modern world. But all the activists are clueless morons manipulated by cynical masterminds, so the message is muddled, and none of it matters anyway once the cannibals show up.
5. The violence is fairly extreme for an American horror movie, but there's really not that much of it; the cannibals don't meet the students until the movie is half over. The movie is not scary at all. It's actually part comedy, in that Eli Roth way. This isn't always a good thing - the stoned cannibal scene is kind of gruesomely humorous, but it also completely takes away any sense of menace or dread the movie had built up.
6. There are some memorable lines in the movie, like "I can smell them cooking my friend!" and "It's good they ate Josh first. He should last them almost a week."
7. The script is not very smooth, and the movie seems like it had story lines cut out of it - there are scenes and characters that feel like they were supposed to be part of something bigger. That's the only explanation I have for the diarrhea scene.
8. The end of the movie doesn't make any sense except to set things up for a sequel. Or else it was Roth's way to deny charges that the movie is racist (I'll let you decide for yourself whether the movie is actually, or intentionally, racist).
9. This is dumb, gory fun, and if you didn't know that cannibal movies used to be a thing, you may be impressed. But it's also kind of boring. And if you're a fan of the original genre, this movie will be pretty tame. It might make you miss the old days when filmmakers didn't care about political correctness or getting the highest box office.