More Complex than the Description Implies *SPOILERS*
The reasons so many people have had issues with this movie are:
1. They can't stomach (pardon the pun) the idea of cannibalism as how it is presented in this movie.
2. They don't understand how the plot relates to East Asian socio-political and gender issues.
While the cannibalism in this movie is hard to watch at points, it is really not meant to be taken literally. It's quite simple. The movie is largely a commentary on the imbalance of the sexes (heavily favoured towards men) and China under the "One Child Policy." All you have to do is think of and notice the line when Aunt Mei aborts the male fetus and says "this is so rare, males almost never get aborted." If you put it into the context of the movie plot, the message is quite literally, "we are eating our women." In China for the past several decades female fetuses are aborted in order to ensure a male heir - most couples if they have a choice will always abort until they get a son. This is, unfortunately, the politics of having a country with over a billion people. India is going through much the same right now.
As for the movie, the plot is a mixture of ancient Chinese folk tales and Western "fountain of youth" tales such as The Picture of Dorian Gray by Oscar Wilde. It is a commentary on the unfair manner in which women in Asia (and the West too!) are expected to be youthful forever while men can age and still attract younger women and be less concerned about their physical appearance (though this seems to be changing in the 2000s). On a "folk" level, it is also a warning against trying to grasp onto miracle "fountains of youth" that cannot stop what is an inevitable process. I hope this will shed some light on the movie, since I think many people are simply looking at it as a "gross" movie based on the cannibalism aspect of the plot. As I said, this is not the easiest thing to watch, but if you put it into the socio-political context in which the made was made, it is actually quite a brilliant commentary on sexism and how it operates.