“The Simpsons” has been so good for so long for 22 minutes at a time that I was a tad wary when I heard that documentary filmmaker Morgan Spurlock (“Supersize Me”) would devote an entire hour to “The Simpsons 20th Anniversary Special: In 3-D! On Ice” (7:30 p.m., Sunday, Fox). But five minutes into the film, I realized I could have spent hours hearing about the show’s history, lore and influence. “The Simpsons” deserves an appreciation of epic length, like the weeklong “Monty Python” retrospective recently seen on IFC.

Spurlock spans the globe to meet with obsessive “Simpsons” collectors and devotees who have covered their flesh with images of Springfield denizens. “Simpsons” creator Matt Groening performs a double take when he hears about a guy sporting a Milhouse tattoo.

Groening also informs us that many Springfield residents are named for streets in his native Portland, Ore., and that Krusty was based loosely on a 1960s Portland TV clown named Rusty Nails.

While often amusing, Spurlock’s film rambles along with a maddening lack of focus. Why spend so much time on a one-time controversy over an episode about Brazil? We hear some mutterings about the show’s perceived anti-Catholic bias from a professional defender of the faith, but absolutely nothing about its continuing fascination with spirituality. For years, “The Simpsons” was the only show where characters attended church or even talked about faith. Serious examinations like the book “The Gospel According to the Simpson” receive no mention.

Nancy Cartwright (Bart) and Yeardley Smith (Lisa) explain the origins of their voices. And Hank Azaria explains how he channeled Al Pacino to come up with the right sound for Moe the bartender. But Harry Shearer — the voice of Burns, Smithers, Flanders, Lovejoy, Brockman, Lenny, Otto, Skinner and Rainier Wolfcastle — is nowhere to be seen.

And except for a few sound bites from Sting, there is no mention made about the show’s role as a showcase for musicians, from Linda Ronstadt to the Ramones to Green Day to the Rolling Stones. The Fab Four never reunited, but the three surviving Beatles (now two) all appeared on “The Simpsons.”

You don’t have to be a critic, or the Comic Book Guy, to find Spurlock’s film both unsatisfying and at the same time wish it would never end.

Spurlock’s film is preceded by “The Simpsons” (7 p.m., Fox) 450th episode, a middling effort about Krusty being displaced by a Disneyfied sidekick (Anne Hathaway) in an effort to attract more young, female viewers.

But even in a subpar outing, “The Simpsons” remains savvy enough to lampoon its place in both the pop culture zeitgeist and on the Fox schedule. The show concludes with the message, “Thanks for 20 wonderful years … Now stay tuned for three Seth MacFarlane shows.”

Today’s highlights

• Luke rescues tots from a monster’s clutches on “Demons” (8 p.m., BBC America).

• Charles Barkley hosts “Saturday Night Live” (10:30 p.m., NBC), featuring musical guest Alicia Keys.

Sunday’s highlights

• “Chuck” (8 p.m., NBC) returns with the slacker-turned-spy endowed with new powers, pushing him, and the show, toward more action and fewer shenanigans.

• Judi Dench returns to “Return to Cranford” on “Masterpiece Theater” (8 p.m., PBS, check local listings), concluding next week.

• The bigamous soap opera “Big Love” (8 p.m., HBO) enters season 4.

• “Ax Men” (8 p.m., History) returns for a third season of logging.

• “Brace for Impact” (8 p.m., TLC) recalls Chesley Sullenberger’s quick thinking during last winter’s Hudson river plane disaster. Harrison Ford narrates.