At the start of “Almost Famous,” which opened Thursday night on Broadway, the frontman of the fictional rock band Stillwater, Jeff Bebe, barks backstage in San Diego that a young Rolling Stone reporter in their midst is “the enemy!”

Under the bright lights of 45th Street, though, the greatest foe of the musical “Almost Famous” is most definitely the film “Almost Famous.”  

Cameron Crowe’s 2000 comedy is a quirky, coming-of-age cinematic gem, which won him an Oscar for Best Original Screenplay, and our fond memories of it — a manic-pixie-dream-girl Kate Hudson, Frances McDormand announcing “My son has been kidnapped by rockstars!” “Tiny Dancer” on the tour bus — are a persistent thorn in the stage version’s side.

Those classic bits are all still here, yes, but they’re a wisp of the original. British director Jeremy Herrin, who should stick to plays and steer clear of Stratocasters, composer-lyricist Tom Kitt and book writer-lyricist Crowe do not present a compelling case for why the film must be a Broadway musical. It’s pleasant and sweet and passes the time, sure, but should that be enough?

Near the end of the show, Sapphire, a member of an elite clique of groupies called the Band Aids, observes that 20 years on, they’ll all remember their time with groovy leader Penny Lane. Perhaps. But the audience completely forgets about “Almost Famous” the musical by 43rd Street.

Semi-autobiographical, Crowe’s stand-in is William Miller (Casey Likes), a meek 15-year-old in 1973 San Diego with a domineering mom and a rebellious sister who encourages his love of rock groups, like The Who. He starts to dabble in music journalism, and gets a chance to interview Black Sabbath for his mentor Lester Bangs’ (Rob Colletti, a funny crank) Creem magazine. 

It’s on that fateful assignment when he meets Stillwater, a middle-of-the-road band that William obsesses over. Even though the guys sneer that the kid is the enemy, he weasels his way backstage by flattering them — and they welcome them into their ragtag family.

That’s dangerous. In the back of William’s mind is hardened Bangs’ No. 1 piece of advice: “Don’t make friends with the rockstars.” Wide-eyed Willy does anyway. And soon he’s assigned by Rolling Stone, who assumes he’s much older, to follow Stillwater on tour for a 3,000 word story. Can he deliver something deeper than a puff piece?

He also gets his first taste of love in the form of Penny Lane (Solea Pfeiffer), a free spirit who is also sort of dating Russell Hammond (Chris Wood), Stillwater’s evasive guitarist.

The plot, exactly the same as the film’s, is not the problem. Coming of age works well in musicals. The No. 1 issue, as it so often is, is Broadway vs. Rock ‘n’ Roll.

Real rock songs from the film’s soundtrack such as Elton John’s “Tiny Dancer,” Cat Stevens’ “The Wind” and Lynyrd Skynyrd’s “Simple Man” are back. Paired with Tom Kitt’s sappy score, which is one Smooth FM number after another, they stick out like an oboe in Metallica.

Kitt has decided on a musical theater soundscape for when characters are offstage to contrast the headbanging. That makes sense. But tunes like “Lost in New York City” and “Listen to Me” have even less edge than his faux-rock music for “Next to Normal,” which was set entirely in an upper middle-class suburban home.

And the lyrics by Crowe and Kitt are dismal.

When Russell and Penny duet on “The Night-Time Sky’s Got Nothing on You,” the married rocker praises, “The way you turn a hotel room into a home.” What is this? A musical or a Marriott ad?

Penny, played capably but not magically by Solea Pfeiffer, also has a clunkier song about her dream of moving to Morocco.

“Do you long for better than this, a way to escape the abyss? Morocco!” it goes and goes some more.

As William’s mother, Elaine, Anika Larsen is eerily like Frances McDormand in voice and mannerism. The actress is maternal and does nothing wrong, but she lacks McDormand’s electric unpredictability.

And the members of Stillwater — Wood as Hammond and Drew Gehling as Bebe are most visible, just as the singer and guitarist would be in reality — amp their gags up the right amount. Most of the jokes are theirs, yet they shrewdly avoid going full Spinal Tap.

It’s not the fault of Wood and Pfeiffer that their characters’ not-so-secret romance drags down the show and feels B-side the point.

They all inhabit Derek McLane’s overly straightforward set, which falls far short of more exciting behind-the-music designs like “Tina: The Tina Turner Musical” or even the final heart-pumping arena scene of “MJ.” Like the scenery, the lights by Natasha Katz are too Broadway and not enough rock concert.

Keeping “Famous” from face-planting is its best find, newcomer Likes. Of course, the 20-year-old actor is helped along by a naturally endearing role, but he plays the part more eagerly than Patrick Fugit did in the film and he has a wonderful voice. He often chooses softness over loud pop stridency, and it’s refreshing to see a Broadway performer in an assembly-line musical have the confidence to hold back.

His number “No Friends,” in which his lonely character wrestles with a desire to be a good journalist and his deeper craving for companionship, is the show’s only good new song.

If there is one thing that makes “Almost Famous” come alive, it’s watching two coming-of-age stories play out at once: One, about a young journalist figuring out his future. The other, about an exciting new Broadway actor stepping out onto the boards.