After a protracted post-production period in which the director fought to put a longer version of the film in theaters, Kenneth Lonergan's sophomore effort, Margaret, is finally being released -- five years later than originally scheduled -- at 150 minutes. Unsubstantiated rumors have surfaced that Lonergan's original cut was an hour longer, and after seeing the film that gossip is easy to believe. Margaret is filled to the brim with ideas. Anna Paquin stars as Lisa, an articulate but emotionally immature 17-year-old Manhattanite with an actress mother and a distant businessman father who lives on the West Coast with his new, younger wife. The film establishes her pampered upbringing (by her own admission, she goes to a school for rich Jewish kids) and her petulant teenage state of mind (she flirts with her math teacher, played by Matt Damon, who confronts her about cheating on a test) with economy and skill. One day, while trolling the Upper West Side for a cowboy hat, she spots a bus driver (Mark Ruffalo) sporting the perfect ten-gallon headwear. She tries to get his attention, and, while distracted, he causes a fatal accident. After the bus driver is found to be faultless, due to Lisa's initial statement to the police, she seeks out the victim's best friend (Jeannie Berlin), and together they find a lawyer willing to bring a case against the bus company and the driver. Meanwhile, Lisa is still dealing with all of the usual stresses in her life, including a nice guy with a crush on her, a jerk who she calls when she's ready to lose her virginity, her mother's habit of picking fights with her so that she can get emotionally worked up enough to act on-stage, her hatred of her father's new wife, and her tendency to verbally destroy any classmate who express the slightest bit of empathy for Muslims (Lisa is still full of righteous anger five years after 9/11). The problem with Margaret is that it's trying too hard to cover too much material, and Lonergan, despite his talents as a writer, needed to pare down his script. There is no central idea carrying the whole movie, so it becomes an unwieldy concoction of social commentary, psychological drama, family dysfunction, and even opera. It's easy to see how this two-and-a-half-hour cut could be streamlined into two different, and very compelling, 100-minute movies. And at the same time, it's possible that the longer version Lonergan was attached to balanced all of this material more successfully. But even as the film loses its way, which doesn't begin to happen until about an hour in, Anna Paquin creates a portrait of a modern teenager so riveting that it's hard to turn away. Lisa's anger is at the heart of practically every scene. She has her reasons for being so furious, and she clings to them with all the tenacity of a young woman who doesn't have the tools to admit how scared she is. She can't comprehend how she feels, so she infuriatingly responds to almost everyone with either a jaded mask of contempt or egomaniacal self-pity. It's a remarkably heavy load for any performer, and Paquin's confident performance is magnetic. She turns Lisa into a richly complex, emotionally feral teen -- as infuriating as she is vulnerable. Lonergan presents a number of scenes, such as a classroom showdown between a nerdy English teacher (Matthew Broderick) and a gifted student over how to interpret a Shakespearean speech, in which he examines how people can misunderstand art and each other. And that may be where Lonergan trips himself up. He's so intent on making sure you understand everything that's going on in Lisa's life that the movie breaks apart from all of his ambition. Without the bus accident, her life would be compelling, and her response to that tragedy is also great material for dramatic storytelling. But it just doesn't add up to a complete film. Lisa doesn't know what to do with her tumultuous feelings -- she's all over the place and, in an attempt to understand her fully, so is the movie. At 150 minutes, Margaret still feels incomplete. But Paquin is so riveting, so warts-and-all truthful in her performance, that the movie will stick with you for longer than it deserves to.