What happens when a great director takes on a generic action movie? “Gemini Man.”

The filmmaker in question is Oscar bookend recipient Ang Lee, who won for “Life of Pi” and “Brokeback Mountain,” and the movie is mostly an excuse to not quite perfect the special effect in which a famous actor is de-aged (the upcoming “The Irishman” will try the same trick on Robert De Niro).

Will Smith plays Henry Brogan, whose plan to retire as the world’s best assassin runs afoul of various covert agencies who hire him and who decide to eliminate him. And who better to knock him off than a younger clone, also played by Will Smith with the help of an expensive-but-unconvincing army of special effects? Called Junior, the younger one looks fine in dimly lit scenes or when he’s wearing a helmet but phony as all get-out in, for instance, a bright walk-and-talk scene where it looks like 51-year-old Smith is acting in a scene with his dead-eyed video game avatar.

Believability is not high on the movie’s list of priorities, but it doesn’t take itself too seriously and everyone involved seems committed to making this so-so material work. Smith likably underplays both roles in this “Face/Off” knock/off, even when his dialogue consists of stuff like, “Scared is good. It means you’re alert,” and other koans from the Tough Guy Affirmation-of-the-Day desk calendar. In addition to himself, Smith gets to act opposite Mary Elizabeth Winstead, who is all intelligence and instinct as a semi-reluctant ally, and Clive Owen, who missed out on playing James Bond but basically gets to play a Bond villain here.

Lee always has been great with actors, but his fingerprints are all over “Gemini Man,” which is much more stylish and surprising than most movies of this ilk. The camera is always in an unexpected place, shooting from an unexpected angle and capturing unexpected textures and colors. I’m thinking, for instance, of an electrifying burst of energy when Smith the Elder pilots a motorcycle down a cramped alley lined with neon-colored buildings. Or another where he’s fast-walking down a street and Lee lets us know there’s a sniper running across the rooftops above him by slyly angling the camera to reveal the sniper reflected in a pool of clear rainwater.

Look, I know no one is going to action movies because of the rainwater, but Lee’s inventive choices make “Gemini Man” seem cleverer, which makes it more fun. And Lee also delivers on the things you’d expect in this sort of movie: speed, car chases, beautiful settings such as Cartagena, Colombia, and Budapest, good guys who never miss with their guns and bad guys who always do. And, in trying to find ways to keep himself interested in this not terribly interesting movie, he also finds ways to keep us glued to our seats.