Danny Boyle's 127 Hours vividly brings to life the much-publicized true story of Aron Ralston, a hiker who in 2003 cut off his own arm after getting it trapped under a boulder while canyoneering in an isolated part of Utah. James Franco plays Ralston as a rad bro with a positive attitude and a love of the outdoors, delivering a tour de force performance that's full of both physicality and nuance.

You'd think that knowing the ending to 127 Hours would rob it of some power, but that foreknowledge actually works in the movie's favor. Knowing what Ralston will eventually do makes his unsuccessful (and heroic) efforts to free himself all the more heartbreaking. These include chipping away the rock with his dull pocketknife and attempting to rig a pulley system to lift the wedged boulder off his crushed forearm.

But before the grim moment when Ralston gets rocked, 127 Hours is an exuberant celebration of physical activity and the great outdoors. Ralston dons his Phish T-shirt, packs a bag and sets out for adventure, along the way bumping into two young female hikers (Kate Mara and Amber Tamblyn) and acting as their guide. Director Danny Boyle, fresh off the Oscar triumph of his Slumdog Millionaire, is a filmmaker known for injecting energy into his work, and the first half hour of 127 Hours is full of quick cuts, swooping helicopter shots and flash-bang montages of everything from Ralston riding his bike across the desert to sipping water out of a saddlebag. It all works perfectly.

I expected Boyle to slow things down once Ralston gets trapped, but his style overwhelms what was potentially a static set. For at least half of 127 Hours, Franco stands trapped under a rock, jabbering into a camcorder and working to free himself. He never really moves, so the film moves for him. As time, hunger and dehydration work over Ralston's mind, they also affect the film itself. Suddenly Scooby Doo is making a cave cameo, and it all makes sense.

A movie like this is going to succeed or fail based upon the performance of the lead actor and the skill of the director. 127 Hours goes two for two. James Franco has been an interesting actor for a long time (Freaks & Geeks fans know the score), but his current run of Eat Pray Love, Howl and now 127 Hours should catapult him to the top of the Hollywood A-list. Franco is on the screen basically the whole time, engaging the audience and taking them along on Ralston's bummer of a trip. Boyle stages the whole shebang in riveting fashion, always making his actor look good while absolutely wringing out the audience.

And best of all: they kept it short. 127 Hours runs a taut 90 minutes. Any more and Ralston's agony would have become the audience's. Any shorter and some of the depth (and the fun of the early portion) would have been lost. I know that watching James Franco cut his arm off will be a tough sell for audiences, but to skip this movie is to skip an exuberant celebration of life.