Maybe 3D does have a purpose; it makes Michael Bay's third Transformers movie worth watching. Not so much because of its illusion of depth as its effect on the editing: the format forces Bay to slow the stroboscopic blurs of the first two films down to longer takes that allow the action to make sense. It even gives Shia LaBeouf — as Sam Witwicky, the feckless liaison between the humans and the benevolent Autobots — a chance to demonstrate some of the aplomb of a CGI-aided Buster Keaton when he spins around a Decepticon by means of a cable hooked in its face. As for the story, let's just say that it starts with JFK saying, "Get NASA on the phone; we're going to the moon!" and somehow involves Chicago getting destroyed by giant metallic shrimp. With funny bits from John Malkovich, Frances McDormand, and Ken Jeong providing relief from the robotic fulminations, this sequel is a little more than meets the eye.