By artistic measures, the fest was more of a mixed bag. At its best, it illustrated the enduring strengths of the indie-rock underground, thanks to spirited and wonderfully idiosyncratic up-and-comers such as Art Brut and Tapes N' Tapes and long-running underground heroes such as Mission of Burma and Yo La Tengo.

But the festival also demonstrated the shortcomings of the often-insular indie-rock scene, offering a parade of acts championed by the influential Pitchfork Web zine. Too many of these bands lacked the charisma to captivate such a large crowd. They celebrated pointless quirkiness and uninspired amateurism, or they were just dreadfully boring.

With a few notable exceptions, the Saturday lineup was especially underwhelming. Things started out strong at 1 p.m. with a fiery set by Chicago's Hot Machines, a hard-rocking garage band whose familiar sounds were distinguished by the considerable energy and presence of fervent frontwoman Miss Alex White. But through the rest of the long and brutally hot day, the only personality as winning as White was Eddie Argos, leader of the English quintet Art Brut.

Argos is a frumpy Everyman and unapologetic schlub -- think of Philip Seymour Hoffman portraying the late rock critic Lester Bangs in "Almost Famous" -- who is determined not to let the fact that he can't sing stop him from taking his band to the proverbial "Top of the Pops." Characterized by their propulsive rhythms and catchy, chant-along refrains ("We formed a band, we formed a band! / Look at us, we formed a band!"), Art Brut delivered one high-energy anthem after another from "Bang Bang Rock & Roll," as well as several new songs that proved that first album was less a novelty than the welcome debut of a group that finally answers the question of what the Modern Lovers would have become if Jonathan Richman hadn't gone acoustic.

Part of Argos' appeal is that he voices the time-honored indie/punk ethic that "Anybody can do it" in such a way that you feel you're hearing it for the first time. At one point Saturday, he noted that he usually tells everyone in the crowd they should go home and start their own bands, "but I'm not going to say that this time, because there are just too many of you! Some of you should start fanzines, or make movies ..."

Sleepy and tuneless

As several of Saturday's other acts droned on, I wished they had pursued those paths instead of music.

Chicago's Chin Up Chin Up offered generic angular guitar rock with so little to distinguish it that each song was forgotten the moment it ended. In contrast, Philadelphia's Man Man (what's with the repetitive names?) was all shtick and no substance, a group of hairy clowns banging on pots, pans and a few actual instruments to evoke Frank Zappa playing cheesy carnival music.

Band of Horses and the Walkmen delivered good but not great Neil Young fuzz and jangle; Destroyer (the other band led by Dan Bejar, the other songwriter for the New Pornographers) churned out fine but not fabulous power-pop, and the Silver Jews delivered interestingly skewed but far from superb country-rock that few would have cared about if bandleader David Berman wasn't known as a friend of Pavement and someone who hardly ever performs live.

The Mountain Goats were just too sleepy and tuneless to deserve any description besides "yawn." At least two of the other acts on the two main stages showed some passion. Ted Leo bled for his art when he accidentally cracked his forehand open on the microphone, but his rollicking set lost momentum when it shifted from driving punk to clumsy reggae. And English dance-rockers the Futureheads overstayed their welcome and became repetitious after about eight songs.

Many of these artists would have been better served by the 30-minute sets scheduled earlier in the day instead of the full hours they were allotted, while Hot Machine and Art Brut could have played for as long as they wanted, as far as I was concerned.

A bit of magic on Sunday

The weather on Sunday favored the fest when the rain abated shortly before the start, and threatened thunderstorms held off for the rest of the day. Much of the music seemed just as magical.

Day Two started strong thanks to the fast-rising Minneapolis band Tapes 'N Tapes, whose leader Josh Grier noted that last year he attended the festival as a fan and stood in the crowd.

Swedish songwriter Jens Lekman and indie-pop band the National both enhanced relatively simple songs with exuberant playing and tasteful orchestral touches, such as horns and violin. But southern New Jersey's odd Christian "family" act, Danielson, only detracted from its material with a gimmicky presentation. (They all dressed in matching uniforms that looked distressingly like a fascist youth organization.)

At the height of another brutally hot afternoon, the now Berlin-based Liars delivered a set of rollicking noise-rock, and Aesop Rock and Mr. Lif offered good-time hip-hop party grooves. Neither set was exceptional, but it might have been a result of the weather: Some music just shouldn't be played under a blazing sun.

Freak-folk guru Devendra Banhart performed his gently lilting hippie campfire music. It was pleasant enough as the sun finally began to set, but it certainly didn't live up to the hype.

At the same time, Wilco drummer Glenn Kotche gave a solo display of his percussive wizardry on the Biz 3 stage. Accompanying himself on electronic loops as he hammered away on an astounding array of rhythmic instruments, he easily matched the layered, trance-inducing powers of any of the weekend's best techno DJs.

Over-30 but oh so hip

Ironically, given media sponsor Pitchfork's role as indie arbiter of all that is uber-hip and cutting-edge, two of the fest's highest points came from acts in their third decade.

Boston's legendary art-punks Mission of Burma were nothing short of incendiary as they mixed classic anthems from the '80s ("That's How I Escaped My Certain Fate," "That's When I Reached for My Revolver") with material from their recent reunion albums that was every bit as fresh and vital. And Hoboken, N.J.'s Yo La Tengo balanced quiet and beautiful pop songs with noisy, full-throttle garage rock as they geared up for the fall release of yet another surprising new album.

Rarely has a band done so much with so little (in the sense of instrumental minimalism) as Yo La Tengo, and it remains a master of the feedback-drenched guitar rave-up.

As the penultimate act of the fest, Austin art-punks Spoon were in a tough spot, after Yo La Tengo and before the much-anticipated reunion of Brazilian Tropicalistas Os Mutantes. But the group kept the focus on its jagged rhythms and slightly askew choruses and acquitted itself well.

As for Os Mutantes, the two brothers who remain from the original trio, the bizarre guitar genius Sergio Dias and keyboardist Arnaldo Baptista, made up for the absence of co-founding vocalist Rita Lee by playing with a wild and magnificent 10-piece band that emphasized the group's earlier, crazier material rather than the later, weaker progressive rock/jazz fusion. The music was gloriously strange and sweepingly cinematic, justifying the group's legendary reputation, and evoking the wild invention of the psychedelic era with nary a hint of nostalgia.

As the high-energy emcee throughout the fest, Hideout co-owner Tim Tuten told the packed crowd earlier in the day that the gathering "wasn't about the music, or being in the park, or drinking beer -- it's about community." Those are idealistic words, of course, but through much of the long weekend, they were indeed true, marking Pitchfork as a model that other Chicago festivals -- including this week's Lollapalooza -- should strive to duplicate.