I had to look up this movie, just to make sure it wasn't a documentary. As one description said, it really tightropes the line between mockumentary and movie. At some points, you think the stars are being very self absorbed, as opposed to being self-effacing. And you start to wonder if it is funny or sad, in a Hollywood "out of touch with reality" sort of way. All you have to do is pay attention to the Ed Begley Jr. segments to see that this is at once, a vehicle for the actors to promote their true feelings, and a way to promote them in a mockumentary format.
It is very much is the improv style of "Curb Your Enthusiasm". As a viewer, if you put yourself in this mode, I think you will find this movie very funny,.