My issue with this film isn't that I didn't understand it. In fact, I would say that it was insanely predictable; my girlfriend and I both figured it out by around the 40 minute mark.
My issue is in the ending, right around the time they pull into the parking lot of the high school. From this point on, the movie abandons any sort of intelligent yet misleading storytelling (typical of Kaufman) in favor of a cheap arthouse short film that destroys any good things this film once had going for it.
If you like psychological films or Charlie Kaufman's other works, check this out and decide for yourself. If not? Don't bother wasting your time, your energy, or your lamentations.
EDIT: The two car scenes that run about 20 minutes each don't exactly help the film's dragging feeling. Yes, it does progress the plot, but yes it is also incredibly boring.