As entertaining as "Gigantic (A Tale of Two Johns)" is most of the time, you kind of wish the filmmakers would have concentrated a little more on the music itself.

The film — a documentary about the quirky, New York avant-pop act They Might Be Giants — often finds itself onstage while the band is performing. And then, frustratingly, it cuts away after only a few seconds.

That's probably not the best way to show those who are unfamiliar with the band and its brand of rather dark and clever pop just how far it has come as a live concert attraction. Still, for the band's intensely loyal legions of fans it's a must-see. And for others, there's just enough to make you want to find out at least a little more.

Think of this film as a musical, cinematic appetizer plate.

"Gigantic (A Tale of Two Johns)" attempts to explain the enduring popularity of the band, as well as trace its origins back to Massachusetts, where the two Johns — the gregarious Flansburgh (the one with dark hair and glasses) and more introverted Linnell (the skinny, soft-spoken one) — met while in school.

They quickly found common musical inspiration and began writing songs together. But to survive in the competitive New York music scene, the transplanted duo (with Flansburgh playing guitar, Linnell the accordion) had to concentrate on the performance side.

Their self-released demo cassette (which was released in a slightly different form later) actually drew the attention of People magazine, while innovative videos for such songs as "Don't Let's Start" got regular rotation on MTV.

But with that success came complaints from fans of "selling out," as did the move to a major record label and the addition of backup musicians (which was pretty much a necessary step to help expand the fanbase and make the band a viable touring act).

Curiously, director A.J. Schnack ends his story the evening before the Sept. 11 terrorist attacks, which, since the film is trying to explore the band's musical influence and not its sociological influence, isn't a bad idea.

Comedians Janeane Garofalo, Andy Richter and Harry Shearer give dramatic readings of the Johns' lyrics, and they're pretty amusing. Same for the behind-the-scenes moments with Flansburgh and Linnell, who are extremely likable.

"Gigantic (A Tale of Two Johns)" is not rated but would probably receive an R for scattered use of strong sex-related profanity. Running time: 102 minutes.