Earth’s climate is screwed, folks like Bill McKibben tell us. If we flatlined our carbon emissions this instant, we’d still have a dark and uncertain future. But Hollywood doesn’t do dark and uncertain. This sci-fi adventure from the minds of mega-star Will Smith and writer-director M. Night Shyamalan proposes a simple, elegant alternative: So we screwed our planet. Let’s find another one!

This endearingly dumb premise is the most interesting aspect of After Earth, and it occupies about 10 seconds of screen time as part of an unwieldy clump of opening exposition. This movie, you see, is not about Earth or the fate of humanity. It’s about a boy becoming a man in the most hackneyed way possible, and about a movie star’s 14-year-old son becoming a box-office draw in his own right.

At least, that’s what Will Smith seems to hope for his offspring, Jaden, who gets most of the screen time in this family endeavor. The younger Smith plays Kitai Raige, a kid living in the shadow of his famous father. His dad is Cypher Raige (wish I were kidding), the awesomest guy in the remains of human civilization.

It’s been a millennium since we ditched Earth, see, and our new home is inhabited by alien monsters who apparently didn’t feel like just giving us their planet to screw up, too. They detect us by smelling our fear, and General Raige has a Jedi-style mind trick for suppressing it, which makes him humanity’s new messiah.

All this is merely backstory to what happens when dad and son crash-land on a strange and forbidding planet — yup, you got it. With Cypher incapacitated by a wound, the kid must brave the posthuman wasteland of Earth to obtain a rescue beacon, while evading an alien that came along for the ride.

What follows is a series of episodic, video-game-style adventures. Kitai grapples with killing night frosts and mutated CGI animals, guided by the humorless instructions of his drill-sergeant-slash-father. Does the boy discover remnants of human civilization and pause to reflect on where his ancestors went wrong? Is there, at least, a twist? Nope. It’s not that kind of movie.

In interviews, Shyamalan has boasted of forbidding Will Smith to use his famous charm. Perhaps he should have helped the actor find something to replace it, because Smith comes off as the world’s most dour motivational speaker in this one-note performance. Jaden Smith, still an obviously unseasoned performer, can’t fill the charisma void.

It doesn’t help that both have been given George Lucas-style stilted dialogue to speak in a bizarre, fluctuating, futuristic accent. If you found the postapocalyptic segments of Cloud Atlas hard to watch without cracking up, you may not make it through After Earth.

This coming-of-age tale could still appeal to kids old enough to handle the PG-13 violence; the adventures are colorful, and Shyamalan succeeds in scaring us with deft editing of the aliens. A more confident, nuanced young actor might have made Kitai’s problems genuinely compelling.

For adults, the movie’s only real saving grace is that, ironically, abandoned Earth looks like a great place to take a vacation. Filmed by Peter Suschitzky, who regularly works with David Cronenberg, it’s all lush, verdant forests and misty vistas, enhanced with digital waterfalls and volcanoes. A few shots are downright magical.

Clearly, the planet has been getting along better without us. It’s not often that a movie makes you think, Good riddance to humanity, but it’s hard to watch the credits roll on this bloated, misconceived project with any other reaction.