Franken Fran is possibly one of the best mangas I have ever read, if only for the psychological and societal implications that it brings into focus.
Rather than a horror or gore manga, Franken Fran is, first and foremost, a satire, a harsh criticism on human society. For instance...
In one episode, Fran meets a girl whose beloved dog got run over by a car. In her goodwill, she saves the dog... by putting its brain into the body of an fat and ugly man. Through the course of the story, the girl, at first abhorrent of her new dog's appearance, eventually grows to accept the dog despite its appearances.
Now, I'm sure all of us have heard the words, "Don't judge a book by its cover," but, really, how many of us follow it? What is most important to the aforementioned story is the reactions of the readers. I, for one, felt enormously uncomfortable the entire chapter, even after the girl accepted the "dog". I just could not help myself from feeling squeamish and disgusted. And, that is precisely Kigitsu's point: we all judge people by appearances, that is human nature. People who do not are outside of the norm.
Finally, in the same chapter, after the dog dies in (what should have been) a heart-rending scene, a Hollywood movie is made of the story. The fat man is replaced with a handsome, youthful guy, and the movie ends with the the girl and the "dog" having sex. Bestiality? Maybe. Commercialism? Definitely. And, again, a point at appearances: something gross doesn't seem quite as gross if it's done by someone hot.
And so, one of the biggest reason I love Kigitsu, and I love Franken Fran, is that there is simply so much to analyze in every chapter. There's always some little subversion or aversion of traditional morals, and there's so many different ways to dissect these themes.