The headline above indicates the first thing you need to know about "The Invention of Lying." About 90 percent of the laughs in the movie depend on people blurting out whatever they're thinking--which is not really the same thing as being unable to lie. The other 10 percent of laughs do depend on people being unable to lie, even when self-interest or common courtesy would dictate not telling the truth.
The second thing you need to know is that only about half of the movie is a comedy. The other half is a pretty somber reflection on what life would be like in a world in which people always tell the truth, even when the truth is painful and sad.
The third thing you need to know is that the movie violates its own set-up, early and often. If you're paying attention at all, you'll notice within about 10 minutes that people refrain from saying whatever they happen to be thinking...even though they're not supposed to be able to do that. If you pay a little more attention, you'll notice two different characters saying things that aren't true in order to ease the awkwardness of a situation--again, something they're not supposed to be able to do. And you'll see one character make, and another accept, flatly contradictory assertions, even though flatly contradictory assertions are supposed to be an impossibility in this world.
Now, for all of you thinking, "It's just a movie!", remember my standard: I will play by any rules a movie lays down, as long as the movie plays by those rules, too. If the set-up for a movie is that in the future, the space program will be run exclusively by Hasidic Jewish armadillos, no problem. You won't hear me say, "Don't be ridiculous. Armadillos can't understand the concept of religion, let alone monotheism. They can't grow those curly sideburns, either. And there's just no way they could run the space program. For one thing, they don't have an adequate grounding in physics." You'll hear me say, "Devout mini-dinosaurs at NASA? I'm in!"
In other words, confronted with a preposterous set-up, I'm totally prepared to say, "It's just a movie. Might be fun."
But if at a crucial plot point, without explanation, there's a tortoise running part of the space program, or a Quaker armadillo running part of the space program, yeah, I'm going to have a problem with that. I'm going to say, "The whole set-up for the film was that the space program was being run by Hasidic armadillos. You can't change that in mid-film without explaining it."
But that's what happens in "The Invention of Lying." I'm not sure if Ricky Gervais didn't realize this or just didn't care, but it made the movie a lot less funny than it could have been.
Footnote: I didn't read any reviews of this movie before I saw it, but I read a bunch after. Can you guess the one hacky thing that almost all of the reviewers did? They very self-consciously used phrases such as, "To tell the truth" and "To be honest," as in, "To tell the truth, I enjoyed this movie more than I expected."
Hysterical. Next thing you know, someone will call Arnold Schwarzenegger "Ahnuld," or maybe even "the Governator." (Oh, and by the way, if I don't post for a while, don't worry: "All be bock!")