For the past year or so, a certain segment of the population—musical-theatre fans who were children in the eighties and thought they were too good for Andrew Lloyd Webber—has experienced a punishing range of emotions about the new movie “Into the Woods,” based on the Stephen Sondheim-James Lapine musical of the same name. The emotions include anxiety, rage, anticipation, possessiveness, nostalgia, suspicion, denial, and dread. More than once, I’ve heard the show’s own lyrics used to explain how “Into the Woods” devotees feel about the adaptation. “Excited and scared,” as Little Red Riding Hood has it.

As a member of this small but fervent demographic, I’d like to explain why we’ve been so tense. Part of it is that “Into the Woods” is easy to get wrong. The musical weaves together fairy-tale figures like Cinderella, Jack (of the beanstalk), Little Red Riding Hood and the wolf, Rapunzel and the witch, and more than one handsome prince. Two new characters, a baker and his wife who’ve been cursed with barrenness, help to tie everything together. By the end of Act I, everyone’s wishes have come true: Cinderella gets her prince, Jack gets the giant’s harp, the baker and his wife get a child, and so on. In Act II, it all falls to pieces. A second giant goes on a killing spree. The princes cheat. The couple resorts to blaming and bickering. The characters question their original wishes and what they stole and whom they sold out to fulfill them. Nobody quite lives happily ever after.

In other words, it’s the antidote to Disney. So how could Disney possibly adapt the show without betraying its dark spirit? That was the question lingering over the buildup to the movie, stoked by dribs and drabs of paranoia-inducing detail. In a Talk of the Town piece by Larissa MacFarquhar in June, Sondheim himself seemed to confirm purists’ worst fears, telling a group of drama teachers that Disney had in fact bowdlerized some plot elements: “You will find in the movie that Rapunzel does not get killed, and the prince does not sleep with the baker’s wife.” (Only one of those things turned out to be true.) Disney’s tagline seemed unnervingly apt: “Be careful what you wish for.”

More than plot, what’s tricky about “Into the Woods” is tone. Lapine’s book tacks between farce and tragedy, winking at the absurdities of the original tales (How the heck does Little Red Riding Hood climb out of the wolf’s belly intact?) and then guiding their characters through calamity and heartache. Sondheim’s score is a puzzle-master’s trove of overlapping motifs, internal rhymes, wordplay (“We’ve no time to sit and dither / while her withers wither with her”), and psychological nuance. Few musical-theatre soliloquies are as elegant as “On the Steps of the Palace,” Cinderella’s deconstruction of the moment she decides to leave behind the shoe:

You think, what do you want?

You think, make a decision.

Why not stay and be caught?

You think, well, it’s a thought,

What would be his response?

But then what if he knew

Who you were when you know

That you’re not what he thinks

That he wants?

And then what if you are?

When the musical opened on Broadway, in 1987, parents would occasionally yank their young children out of the theatre in shock during the second act, thinking, They killed Rapunzel? I was too young to go (though, to my mother’s credit, she brought me to see Sondheim’s “Passion” a few years later), but fortunately Lapine’s note-perfect production was preserved by “American Playhouse.” The moment I first saw Bernadette Peters singing “Last Midnight” on PBS, circa fifth grade, was a formative one. It wasn’t just that she looked like a fabulous goth diva or her peculiar, warbly way of delivering punch lines. It was Sondheim’s articulation of the witch’s alienation and moral skepticism that was so riveting. Also, her hair.

I certainly didn’t comprehend all the musical’s resonances, among them the communal solidarity during the AIDS crisis, which at the time was stomping around the theatre world like an angry giant. (Sondheim has downplayed the AIDS connection, but it’s unavoidable.) Still, the show was a psychological bait and switch, a gateway to adolescence and its complicated truths. Act I had magic beans. Act II had disillusionment, responsibility, and loss. You got from one to the other through the woods, as good a metaphor as any for the big brutal world. Even the shifts in tone were a lesson: amid despair, a dry one-liner (“I was raised to be charming, not sincere”); after an act of courage, ethical revisionism. What I learned from “Into the Woods,” most of all, was ambivalence. It’s in every song, undermining prepackaged morals. (“Isn’t it nice to know a lot?” Little Red sings to herself. “And a little bit not.”) No one in musical theatre does ambivalence like Sondheim, and usually no one tells you what it is until after you’ve experienced it. Cinderella’s hemming and hawing on the palace steps is worlds away from “A Dream Is a Wish Your Heart Makes,” from Disney’s cartoon version. What if your heart doesn’t have a goddam clue?

It’s appropriate, then, that ambivalence is the overriding feeling I’ve had about the movie, even after seeing a screening a few weeks ago. Rob Marshall’s version, I’m happy to report, is faithful enough to please most diehards, without sacrificing the concrete magic that movies can offer. For the most part, the plot changes seem wise. (Come on, guys, relax about the Mysterious Man.) Meryl Streep is excellent; duh. It’s wordier and weirder than other movie musicals, as it should be. If anything, it was jarring to see the show's ambiguities translated so literally to a big holiday film, where they don’t seem to belong—or maybe I was just seeing the musical's flaws for the first time. Is the second-act massacre really deserved? I kept wondering, as I watched, how this could possibly be marketed to children, but then I reminded myself that I was ten when I saw “Into the Woods” on PBS. So now I’m worried less about the movie than about how the rest of the world will receive it—the selfishness of aficionados, who want their special thing all to themselves. Someday, the generation that learned about moral relativism from “Wicked” will feel the same way. I’ll tell them something that I learned from the witch: sometimes the things you most wish for are not to be touched.