The Invention Of Lying was based on an interesting premise, what would a society be like without any sense of the make-believe? The movie followed the idea that whatever someone said was true must be true, but that requires something impossible: a perfect representation of the inner-self. Take a society of completely honest people who can't lie there would still be the need for detecting falsehood as brains aren't perfect. So logically speaking some things would still be wrong.
Of course it's just a movie, and as far as films go I enjoyed it. Had a few laughs and found a few things to think about.