Firstly, ignore the synopsis, which was yet again written by someone who hasn't actually seen the film, and misses the point completely.
Secondly, if this sounds like the kind of movie you might want to see, check out Georges Franju's Surrealist masterpiece "Les Yeux Sans Visage" first, because this film rips off a great deal from it without being anywhere remotely near as good. Then watch this one if you're some kind of obsessive cinematic face transplant completist.
Thirdly... well, frankly, where do I start? By telling you that the "hero" spends almost half the film being so obnoxiously selfish that he makes "Green Lantern" look like "Forrest Gump", and the rest of it being maybe 10% nicer? By pointing out that in 1966, a doctor whose entire job consisted of replacing the lost body-parts of damaged people with realistic-looking prostheses probably wouldn't have considered supplying a rubber mask to a man with hideous facial scars so that he could leave his house without wrapping his head in bandages precisely equivalent to the fictional Baron Frankenstein's corpse-reanimating crime against God? By saying that mild mental retardation doesn't turn people into subhumans who have extra senses because they're animals?
I get that 50 years ago, Japan was such an intolerant society that if you had anything whatsoever wrong with you, you were literally a "monster", and this is a ham-fisted protest against such attitudes. But since it also states that physical injuries damage your soul, and any cosmetic alteration that makes you unaccountable to the laws of a repressive society automatically turns you into an amoral psychopath, I fail to see what point is really being made here. Cosmetic surgery is evil, possibly? I really don't know.
This is an ugly, mean-spirited, depressing film, and the random touches of pretentious but irrelevant Surrealism add nothing. Avoid.