It’s not great science fiction, but I Am Number Four gives young-adult movies the vibrant heartbeat that the genre will be searching for once Harry Potter finally exits this summer. One of the few survivors of his destroyed planet, Number Four (Alex Pettyfer) grows up on Earth while he’s on the run from intergalactic baddies. The struggle makes its way to rural Ohio, where, as high school student John Smith, Number Four falls in love, and decides to stop running. Yeah, it’s fluff, but it’s well-assembled fluff (courtesy of D.J. Caruso). The young cast (Pettyfer, Dianna Agron from Glee and ass-kicking hottie Teresa Palmer) raises the material a notch or two.