Here's a movie that teeters on the edge of being really pretty good and loses its way. I'm not sure quite what goes wrong, but you can see that it might have gone right. Maybe Paul, its alien hero, should have been sent back to the shop for a rewrite. He isn't merely voiced by Seth Rogen, he is Seth Rogen, if Seth Rogen looked like your usual bulb-headed, big-eyed being from outer space.