The unreliable narrator of the novel, a governess charged with caring for two children who may or may not see the ghosts she sees, invites the reader to flip-flop between thinking her a lone protector against unspeakable evil and a greater threat to the children than any spirit.
Presumably they were wary of messing with a solid gold classic, but while "Oz" does present a wide target for critics, they shouldn't have worried: Director Sam Raimi ("The Amazing Spider-Man, " "The Evil Dead") takes care to honor the original in spirit and in style.