I read the book, didn't find it particularly memorable or well-written. And Norman is quite different -- he's still a mental case with a split personality, but even his "normal" self is criminally inclined. (He hasn't black out his mother's murder from his memory -- he knows he killed her but thinks he resurrected her with black magic.) This makes him less sympathetic, so the whole story is less of a dramatic tragedy, more of a simple exploitation horror story.
When I interviewed him about it, screenwriter Joseph Stefano (who adapted the script for director Alfred Hitchcock) said the only things the book had going for it were the surprise death of Marion and the unguessable twist ending.
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