Finally dug up my book, this is what it has to say:

Spacek attempts suicide... ...When Spacek recovers, the fantasy starts... ...begins to take on Duvall's personality... ...Duvall, appalled but unable to resist, becomes at the same time drained... ...first waiflike and later (metaphorically) almost invisible. This apparent psychic vampirism is a disturbing tour de force. As a fantasy of the mutability of personality... ...is as startling in its way as, say, the overt science fiction of Invasion Of The Body Snatchers.

Peter Nicholls - The World of Fantastic Films An Illustrated Survey.

I don't mind the classification as Fantasy, but I would not do it myself.

In fact I think the author has it wrong: since Duvall was invisible before. Nobody paid attention to her till Spacek gets there. And Spacek is not stealing Duvall's actual personality, rather her imaginary one.

The last change at the coda is apparently a positive one for both Millies. Bringing Willie into the equation makes all three more than the sum of their parts. ANd therefore not quite vampirism/parasitism.

"There is a lot of money tied up in this film and people expect to hear a boom when something blows up, so I'll give them a boom."

George Lucas as quoted by Harlan Ellison's WATCHING
Last Edited By: hermanthegerm Apr 23 10 9:45 AM. Edited 3 times.