Jeff Ford went to see Apocalypto, and offers his take (undoubtedly better than the movie*). The bottom line is probably this:
If you're not partial to the sight of hearts being ripped out while still beating and being shown to their previous owners, you might not want to check this out.
*Which I will see, absolutely, not because I particularly think I'll like it or it'll be good**, but because I've been reading a lot about that part of the world during that period and I want to admire the make-up and costuming and spectacle of it.
**Actually, it sounds like it probably is good in the way you go see a "good movie," but not in the way I necessarily mean here.