Director Andy Muschietti was smart to focus on the adolescent half of Stephen King’s “It.”

There, we fall for the seven kids who are known as “losers.” Set in 1989, the thriller pulls you into its world (either through nostalgia or sheer charm) and never lets go – particularly when the seven join to battle their individual demons.

A clown named Pennywise (Bill Skarsgard) is at the heart of all of it. He first grabs one boy’s brother, then masterminds the nightmares of the others.

By the time the gang unites, the goal is clear: Seek and destroy.

Muschietti does much with King’s seven deadly sins. He isn’t afraid to taunt the kids in the worst way and doesn’t hold back when it comes to bullies. Looking a bit like older versions of the tormenters in “A Christmas Story,” they have their demons, too, and account for much of the film’s violence.

While 12- and 13-year-olds would love this, it’s rated R for a reason, not the least of which is Finn Wolfhard’s penchant for swearing. A regular in “Stranger Things,” Wolfhard gets the best lines, largely because he rages at tyranny that comes in the form of guys with switchblades.

While Jaeden Lieberher struggles with his character’s stutter and Sophia Lillis looks a bit too much like Amy Adams for her own good, they make a great couple, able to give first love the innocence it deserves.

Like “The Goldbergs’” Adam Goldberg, Muschietti embraces the 1980s with gusto, filling his sets with so many touchstones you’ll feel like he knew Doc Brown and had keys to Marty McFly’s DeLorean. When he delves into the story’s horror lining, “It” isn’t as secure as it should be.

Some of the moments are stirringly effective. Others are just headscratchers.

When Jeremy Ray Taylor is roughed up by the toughs, our heart bleeds. He’s the overweight friend who has clues to all the strange events going on in Derry, Maine.

By studying papers in the town’s library, he’s able to create a NCIS-level dossier that helps the others find the source of their woes.

While Skarsgard is truly terrifying, part of his fear factor depends on that oh-so-creepy Oscar-worthy makeup. He’s even scarier than Tim Curry in the TV miniseries version of King’s book.

While that edition tried to stuff more than 1,000 pages of terror into its running time, this “It” holds back, promising plenty for a sequel.

There, we can see Adams, Jerry O’Connell, Ben Stiller and others playing out the drama. Muschietti doesn’t need to pull a “Boyhood” and wait.

There are plenty of actors who can morph into the adults. And Skarsgard is more than ready to continue the journey. He’s “It” and so much more.