Do we really need “United 93?” The question is on a lot of people’s minds as the fifth Tribeca Film Festival opens tomorrow night with Paul Greengrass’s harrowing speculation about what transpired aboard the hijacked airplane that crashed in Pennsylvania on September 11, 2001. The festival is to be commended, even marveled at, for such opening night audacity. It’s about to kick off the festivities by traumatizing several hundred people with a blast of unbearable, nerve-shattering verite.

Savvy, ambitious, and beyond precocious, the TFF is still in its internship phase. Joining the ranks of international mega-festivals like Berlin and Toronto seems extremely unlikely at the moment, but this is New York, and we don’t like to be told what we can and cannot do.

Whether or not Tribeca wants to be a worldclass festival is another matter. Its priorities have always been split between movies and marketing, cinema and cheerleading, auteurs and American Express. For the moment, this still makes for a bit of a mess, but the festival is poised like no other in the world to maximize its access to money, the press, and an eager population of moviegoers.

Hatched from the crater at ground zero, the festival has since mutated into a benevolent blob, each year expanding its geographical reach. It now stretches all the way to the AMC Loews Lincoln Square and seems ready to swallow up Lincoln Center. Is the New York Film Festival nervous yet? It should be.

The one thing Tribeca has succeeded at is injecting a fresh idea into the city’s bloodstream. We may not need so many middling indies on the program, the world premiere of “Poseidon,” or a panel discussion on “The Biology of King Kong,” but we do need the possibility and potential of Tribeca, the challenge it poses, and, of course, the movies it projects.

As for “United 93,” you can argue about whether it should have been made in the first place, but not whether it could have been made much better than this. Mr. Greengrass is a supremely scrupulous craftsman, and whatever else it does, “United 93” exhibits virtuoso restraint in the execution of its agonies.

“United 93″opens for all to see (or avoid) this Friday, and you won’t have to wait long for other big titles like “Mission: Impossible III” and “Poseidon” to arrive at the multiplex. But you might want a get a jump on “Lunacy,” a crazy new vision from the Czech surrealist Jan Svankmajer, due at Film Forum at the end of the summer. Inspired by Edgar Allan Poe and the Marquis de Sade, this excellent jolt of blasphemy interrupts its gothic narrative to spy on the animated antics of raw meat, severed tongues, and autonomous eyeballs.

Claude Chabrol teams up with Isabelle Huppert for “Comedy of Power.” But if you prefer music to mise-en-scene, the glut of rock docs continues full blast with movies about the Pixies (“loudQUIETloud”), the Wu-Tang Clan (“Rock the Bells), the Iranian music industry (“Sounds of Silence”), and the U.S. Air Guitar Championship (“Air Guitar Nation”).

Politics is everywhere. “A Flock of Dodos” skims over the intelligent design controversy. Even the brouhaha over the Jets stadium gets its own movie (“A Stadium Story: The Battle for New York’s Last Frontier”).

To put it simply, if you exist, there’s a movie at Tribeca for you: Iranian transsexual (“Inside Out”), avant-gardist (“Jack Smith and the Destruction of Atlantis”), horror buff (“Sam’s Lake”), ecstasy dealer (“Fifty Pills”), filthy rich (“The One Percent”), sci-fi nerd (“The Sci-Fi Boys”), fat girl (“Fat Girls”).

All things to all people, or not enough for no one in particular? The best approach to Tribeca, like the city itself, is to ignore what everyone says and figure it out on your own. What good would a real New York festival be if it didn’t baffle, delight, overwhelm, and provoke?