About an hour and a half into Richard Linklater’s memorable new film, my notes say, “This is RIVETING.” Exactly one hour later, as the movie finally ceased (“ended” is too strong, too decisive), I breathed a sigh of relief. What went wrong to turn the movie from startling, luminous journey into boring, platitudinous slog?

Linklater’s movie has gained a lot of press for one of those gimmicks which hide deep meaning under their showy surface, like the delays in Hamlet. Linklater shot the movie over the course of 12 years, so that as Mason Jr. (Ellar Coltrane) grows from age five to freshman year of college, Coltrane grows with him. So does sister Sam and her actress Lorelei Linklater. The device offers a fresh, striking way to show continuity and discontinuity in our lives: No matter how many homes, friends, even family members we shed, our faces are very hard to entirely leave behind.

The movie’s strongest scenes come early, when Mason Jr. is still a little boy. His parents (Patricia Arquette and Ethan Hawke, both terrific) have already split up. He rambles through the neighborhood in the company of a slightly older boy who takes him graffiti-painting. He listens to his mom fighting with her new boyfriend; he suffers the injustices of a Britney-singing, fake-crying sister. These short sequences swing perfectly from painful to hilarious and back.

Throughout the movie the adults in Mason Jr.’s life will try so hard to educate and discipline him–to teach him to bowl, to win girls, to clean up after himself, to express his emotions, to share his father’s politics–but he keeps escaping them. This portrayal of the goodness and normality of the unsupervised parts of childhood has become sadly countercultural.

The theme of leaving the past behind surfaces immediately, as the mother announces that the whole family is moving to Houston. Sam’s response is perfect: “No, mother!”, punctuated with these bizarre little-kid popping noises she makes with her lips. Every second is believable, and difficult–from Mason Jr.’s quiet question, “What if [my dad] wants to find us, and he can’t?”, to Sam’s run-on declaration, “Goodbye house we’ll never see again and I’ll never like Mommy as much again for making us move!”

Nearly the only thread of continuity (outside the film’s central family unit of the mom and her two biological children) is Mason Sr. The kids’ dad is a blowhard and a jackass, and it’s easy to see why a woman would leave him–but it’s easy to see why a woman might love him, too. He’s a “man’s man” who is never cruel; he offers what I think is the only explicit apology in the movie, after badgering his son for getting frustrated at a bowling alley. By the end of the movie he was probably my favorite character, just because he endures quite a bit of humiliation for the sake of his family.

With so much going right in this movie, how does it all go so wrong? There are slight missteps, like the political pandering (Democrats can be silly, but Republicans are Confederates who threaten children) and the Nice White Lady moment between Mason’s mom and a Latino laborer, but the major mistakes are three.

First and most basically, Mason the teen is just kind of boring. The movie slams to a halt when he hits about tenth grade and never recovers. We get acres of teen philosophy (“I just want to be able to do anything I want, just because it makes me feel alive, not because it gives me the appearance of normality”) and the stakes suddenly feel very low.

That’s because of the second problem, which is that Mason never does anything really wrong. He’s a prototypical good-but-aimless kid. We see his foibles–he’s a bit surly and a tad whiny, he smokes some pot if you consider that a foible, he comes home late at least once which possibly makes his mom cry, he sometimes fails to do his homework–but no real sins. He’s bullied but never bullies back. His sister at least gets to be snotty about her grades, which makes her seem like a real person. Where’s the casual cruelty of childhood, the hurtful rather than just boring narcissism of adolescence, the misdeeds which will only be acknowledged and regretted years later? I mean, I get that “Boyhood” isn’t “Carrie,” but must it be “Annie”?

This failure of realism has knock-on effects, like the way the other characters all rush to praise Mason and his mom. “Your mom is so smart, and so caring”; “You’ve got a good heart”; “You have a real talent.” A small portion of that is adults trying clumsy manipulation techniques, hoping to soften Mason up, but far too much of it is sincere. Mason Sr tells his son, “I wasn’t the least bit concerned with the state of your soul,” and for the audience, that’s the problem right there. Mason and his mom seem to fade and become generic as they grow older and nicer, as if every compliment wears off another layer of specificity.

And the final problem is that as Mason nears college age, the Meaning of Life begins to rear its horrid head. And the meaning of life, it turns out, is that we feel stuff. Parents are just as confused as children, which is true but not wildly interesting (and the ways in which it’s false are often more interesting than the ways in which it’s true). There’s no actual arc: no “Sunrise, Sunset” tale of taking one’s place in the chain of generations; no tale of surviving and recovering from parental mistakes; and not even a tale of how these two stories interweave, so the apple always falls, against the laws of physics, simultaneously far from the tree and too close. And so the movie feels weirdly static, despite its emphasis on the one-way arrow of time.