Broken Base: The excruciating detail the movie goes into showing the war crimes. While such horrific acts did indeed happen, some have argued that, like films such as The Passion of the Christ, the film focuses too much on them, and not enough on the actual victims or perpetrator's reasons for doing so, making the whole thing come across as exploitative rather than informative.
Fridge Horror: Not only did the war crimes depicted in the film actually happen, they were actually worse in real life.
Nausea Fuel: The pressure chamber scene. Frankly, if a man's intestines squirting out of his anus doesn't warrant Brain Bleach, it's hard to conceive of what does.
Sequelitis: The film was followed by several (unconnected but thematically similar) sequels, consisting largely of retreads of the original, right down to entire scenes being recreated. This was completely averted by the film's fourth sequel, which pulls away focus from Unit 731 to focus on the Nanking Massacre.
The part where a cat gets eaten alive by a horde of rats seems to be the movie's most infamous scene, mainly because it caused debates over whether or not the sequence was real. note It isn’t. The cat was covered in a mix of honey and fake blood, given some fish, and sent home afterwards.
The vivisection of the mute boy, since the scene is spliced with actual autopsy footage.
Squick: The experiments. All of them. Also the fact that the rats were actually set on fire and killed during the filming.
Too Bleak, Stopped Caring: Apart from the graphic gore, there's also the fact that the main characters are all heinous war criminals who never receive any kind of comeuppance for their actions. Combine these with the fact that there's very little attempt made to humanize either the victims or the perpetrators, and you get a film that has widely been criticized as being exploitative rather than informative.
