Obviously with a running time of 4.5 hours, this is not an easy watch, but considering that 3 hours of the movie is pure human atrocity, this will try both your stomach and mental capacity. I watched the opening 1.5 hours, went away and came back to finish the filma pseudo documentary.
I had two complaints with the film. From the little I know on Unit 731, most of the experiments were carried out on Chinese prisoners, but the film only featured Caucasians. The other complaint was the effects. It's too bad they weren't better since the bodies often looked like plasticine.
The sound effects and music were perfect, and the last hour was an interesting touch (I won't spoil it, but I will say this: It was a complete left turn from the first three and a half hours).
If I had to pick one word to describe this movie, it would not be extreme, or gore, or sickening (but all three would make great descriptions), but simply: deliberate. Each scene is played out in deliberate excruciating detail. Case in point is the opening scene walking through the snow for five (?) minutes and the scene where the man is freezing outside.