A RECENT subplot on Glee features an anguished dad trying to quash his son’s dreams of becoming a professional dancer because, he reasons, show business is so fickle. And indeed it is—as Fox has witnessed to its chagrin this fall.

A rare TV/music double sensation just last year, Glee—an over-the-top romp about a high-school show choir filled with colorful characters—has officially entered its awkward middle years.

Some of the stats are about as inviting as pimples and braces. Glee has shed 23 percent of its audience compared with last season even after DVR viewing is factored in, according to Nielsen. A 3D movie tie-in was released in August and drew disappointing box office. Sales of the Glee albums—13 in all, featuring the show’s signature, chorus-style covers of pop hits—have plummeted lately compared with earlier efforts.

The deflation has been “kind of surprising,” said Brad Adgate, an analyst at ad firm Horizon Media, given that the show is only in Season 3 and that for the rest of its schedule, Fox has seen big gains this fall compared with last year.

But network and studio brass bristle at any suggestion that the show is hitting sour notes.

“Across the board, network television has with many returning shows had sort of a slow fall,” said Dana Walden, chairman of the 20th Century Fox Television studio, which makes Glee as well as The Simpsons, Modern Family and many other shows. “There’s a very broad, healthy audience for this show.” Sales of Glee music sunk when the cast dipped into the Broadway songbook earlier this year, but the franchise just scored another huge iTunes hit with a mash-up of Adele’s “Rumour Has It” and “Someone Like You.” The track got 160,000 downloads its first week, according to Billboard—one of the biggest tallies ever for a Glee number.

“Just when people were kind of suggesting that the show had kind of peaked on the charts, out comes this moment, this single that really catches fire,” said Keith Caulfield, associate director of charts and retail at Billboard. Overall, Glee has sold an astonishing 6 million albums and 30 million single tracks, according to Nielsen SoundScan—making the Glee kids one of the most successful musical acts of all time.

Whether the TV ratings pick up or not, studio executives point out that the show is a virtual lock for a fourth-season renewal, thereby ensuring it the riches that await in syndication to local TV stations or cable networks. Walden said she was “not only optimistic—I feel confident” that Glee will be back next season. (Although the cast may look slightly different: Some characters will likely be graduated out of the series, although Walden said specific decisions will be made as this season winds down.)

Back in February, Fox gave Glee the plum post-Super Bowl spot—traditionally reserved for a series that network executives believe can grow further with mass exposure. Glee drew more than 30 million viewers, by far its highest audience.

Even so, there’s little question that the Glee phenomenon has hit a junior-year slump. The show is averaging 10.3 million total viewers this season, down 23 percent compared with last year. And in its all-important adults 18 to 49 demographic, Glee is off by 21 percent, which indicates young viewers—the ones who drive most cultural trends—are cooling on it. That may leave behind a smaller audience of “Gleeks,” the preferred term for hard-core fans.

Fox—which launched Glee in 2009 with a painstaking series of marketing maneuvers—may have overpromoted the show as a pop-cultural sensation, Adgate believes.

“The show has been stretched, perhaps causing some fatigue,” he said. “The concert tours, movie, CDs, downloads, [a] reality show on Oxygen.”

And then there’s the show itself. Popular as the distinctive Glee musical numbers have proven, opinion has always been sharply divided on the merits of the rest of the series.

“Since the first season, I’ve been indecisive about Glee; the writing is inconsistent, the episodes are uneven, and enjoying Glee always raises questions about whether or not the show is good or simply a shiny object,” wrote Elizabeth Wiggins on the entertainment site popmatters.com. Other critics have found that Glee doesn’t quite pull off its mix of comedy, drama and music and that its characters are too over-the-top—including super-villainous coach Sue Sylvester (Jane Lynch)—to be believable.

Last year the show gorged on special guest stars, such as Gwyneth Paltrow, and themed episodes, including a highly rated Britney Spears tribute. Such stunts may have brought in extra viewers, but sometimes they also irritated fans.

Kevin Reilly, Fox’s entertainment president, told USA Today recently that Glee had “frayed creatively” due to excessive storytelling tangents. The comment irked Ryan Murphy, the show’s co-creator and guiding light, according to an insider who spoke on condition of anonymity. It’s a diplomatically volatile situation because Murphy, previously best-known for Nip/Tuck, is also behind American Horror Story, the new series for FX, Fox’s sister cable network. (Neither Reilly nor Murphy would speak for this article, according to spokesmen.)

Fox TV’s Walden explained that the network and studio brass merely wanted a return to the basics.

“What we asked Ryan to do this season, particularly at the start of the season, was to focus less on guest stars and to shine a very strong light on our core cast,” she said. “It was not in reaction to anything. It was looking at the big picture of Glee and looking at the potential that this show has.”

In the most attention-grabbing episode this season, entitled “The First Time,” the show teased viewers with the possibility of two consummated romances, one straight and one gay: singing star Rachel (Lea Michele) and her sometime boyfriend Finn (Cory Monteith), and Kurt (Chris Colfer) and his boyfriend Blaine (Darren Criss).

Although there was no nudity and the subject was handled discreetly by TV standards, some critics slammed the episode for what they said was promoting teen sex. CNN.com complained of a “brazen, ratings-boosting publicity” ploy. Walden replied: “Our core audience was very happy with that episode.”

The irony, of course, is that Glee’s numbers are actually down. But a less-potent Glee still has much more power than the typical TV show. It’s not just Gleeks who say the series is nowhere near its final curtain.

“As with any phenomenon, it’s going to sort of cool off,” Billboard’s Caulfield said. “Glee has probably just come down to normal popularity, as opposed to stratospheric popularity.”