Magic Mike, Steven Soderbergh, 110 mins (15)Seeking a Friend for the End of the World, Lorene Scafaria, 101 mins (15)Electrick Childre, Rebecca Thomas, 96 mins (15)

This male stripper's story starts joyfully but swings to the judgemental half way through

If films had intervals, I'd advise you to use the interval in Magic Mike to leave the cinema and head for home, or better yet for the nearest strip club. The first half delivers just as much fun as you'd expect from a comedy drama about a troupe of male strippers, and twice as much fun as you'd expect from any film directed by Steven Soderbergh. The second half is where the magic fades.

Inspired by Channing Tatum's own experiences, it stars Tatum as a roofer-by-day, stripper-by-night in Tampa Bay, Florida. When he meets Alex Pettyfer, a 19-year-old drop-out, he takes him under his muscular wing and takes him along to a revue bar run by Matthew McConaughey.

Soon, Pettyfer is dropping his trousers with the best of them. It's the time-honoured Hollywood tale of a youngster who's introduced to the glamour of showbusiness by a kindly mentor, except with more group sex and penis-enlargement pumps.

Magic Mike doesn't shy away from the seediness and shallowness of its characters' hedonism, but it isn't judgemental, either. Part celebration and part good-natured mickey-take, it's a breezy, laidback lark of a film, with a disarmingly dopey leading man and a nicely tentative relationship between Tatum and Pettyfer's sister (Cody Horn), who's wonderfully unimpressed by what it is the men in her life do every evening.

But the movie's trump card is McConaughey, who follows Killer Joe with his second career-defining role in a month. McConaughey, who doesn't wears shirts in films if he can possibly avoid it, is terrific as a man whose lifelong devotion to titillating women has driven him to the verge of slavering madness. His fabulous opening monologue about the club's no-touching policy guarantees that strangers in the street will shout "Can you touch this?" at him for years to come.

For a while, it's a pleasure to hang out with these guys, and even more of a pleasure to watch them let it all hang out. But after an hour, you start to notice that Magic Mike doesn't have a plot. And at the same time, the film-makers appear to notice it, too. All of a sudden, a crisis involving vindictive drug dealers crashes in from nowhere, while the dialogue takes a newly pious stance against stripping. We're supposed to accept, at this late stage, that it's a degrading and soul-sapping way to make a living, even though the shows we've seen – and we see plenty – are witty, disciplined, astoundingly athletic, and altogether a cracking night out.

The film's moralistic turn betrays the buoyant liberalism that has made it so enjoyable until then, and it's also a betrayal of the characters' true talents. Tatum's dream is to become a furniture designer, but, from what we've been shown, he's far more gifted at being a Chippendale than he is at making Chippendales.

Seeking a Friend for the End of the World is conventional in having two near-strangers, Steve Carell and Keira Knightley, take off on a road trip to be with their loved ones, only to realise that the person they really love is on the other side of the handbrake. Knightley's floaty-dress-and-anorak-wearing kook is its most clichéd element: in indie romantic comedies, gorgeous weirdos like her are always attracted to uptight, lonely men. In reality, I doubt that phenomenon is common.

Less familiar is the notion that the Earth is just three weeks away from being obliterated by an asteroid. What's bold about this premise is that Lorene Scafaria, the writer-director, never once suggests that the planet might be saved. Instead, she gives us a sardonic, eerie vision of the ways we might react to the knowledge of our imminent extinction, and she does so without letting the film become a farce or a tragedy.

For some people, the apocalypse is no reason to stop going to the office or mowing the lawn; for others it's a cue to try heroin. Grounded by Carell's reserved, awards-worthy performance, Seeking a Friend … is tinged with melancholy, but also with optimism, which is tricky for a film about the extinction of life on Earth.

There's another offbeat romance in Electrick Children, a captivating, original fairy tale about two teenagers who go on the run from their religious sect in Utah and are adopted by a group of grungy Las Vegas skate-punks, including Rory Culkin. Expect to hear much more of its first-time writer-director, Rebecca Thomas, and its big-eyed starlet, Julia Garner.