AT LEAST for an hour or so, "The Gunman" looks like it might be pretty good - a well-made, politically aware action thriller that makes up for its generic plotting with an outstanding cast and sharp, keenly observed atmospherics.

Then it all just goes kerblooey and nobody gets out unscathed.

Before it flies fatally off the rails, Sean Penn fuses seamlessly with his character, a sharpshootin' international-aid worker named Jim Terrier, whose macho bona fides and pugnacious idealism play perfectly into Penn's off-screen persona.

Penn takes every opportunity he can to strip down in "The Gunman," the better to show off an impressively buff torso.

He also makes sure that this story - directed by Pierre Morel and based on Jean-Patrick Manchette's novel - always puts him on the side of the angels, even when bullets fly, fists crack, knives impale and bombs explode with promiscuous abandon.

After all, Morel is the man who so memorably helped resuscitate Liam Neeson's career with the surprise 2008 hit "Taken." But anyone taking a cue from that mid-career resurrection may want to consider the recent box-office take of "Cinderella," which soundly beat "Taken"-knockoff "Run All Night" when the two films opened alongside each other last weekend.

And they'll surely want to commission a script that makes smarter use not just of Penn - who manages to exert unbeatable screen charisma no matter how ludicrous the movie - but of his co-stars, including Mark Rylance, Ray Winstone, a hammy Javier Bardem and the lovely Italian actress Jasmine Trinca, who injects a welcome note of earthy realism to her otherwise rote role as romantic foil.

Say this for "The Gunman": It looks terrific, hopping the globe from the Democratic Republic of Congo (played by South Africa) to Gibraltar to Barcelona.

Unfortunately, as the plot progresses, the action and Terrier's over-determined character arc, including a lamentable physical side-effect of his dubious career, become exponentially more outlandish.

It all comes to a preposterous head in a climactic scene staged in the storied Spanish toreadors arena known as La Monumental, where the filmmakers try mightily for thrills and metaphorical weight, but fail on a scale commensurate with the setting.

"The Gunman" may start as a genre exercise of promising purpose, but it winds up being just a lot of bull.