Let's face it, kids. At the Drive-In ain't getting back together any time soon. The so-called hiatus of the best post-hardcore band of the late '90s/early '00s seems alarmingly permanent at this point and the two "side projects" are beginning to look more like opposing sides of a bipolar disorder.

Case in point: The Mars Volta's July 16 appearance at The TLA. Sure, the opening battle march of "Inertiatic ESP" saw singer Cedric Bixler and guitarist Omar Rodriguez rocking the same psychotic energy that turned many a head back when they were in ATDI. Wasting little time tossing his microphone stand into the wings, Bixler wailed a chilling falsetto before dropping to the floor to do the worm and convulse-dance like a demon possessed. Rodriguez, stage left, churned out rapid off-tempo riffs in between spinning his axe over his shoulders and crouching to attack the upper fretboard with his wrist, all the while his towering afro blowing in the fan-generated wind like he was a crazed arch villain in a bad '70s cop movie.

The two front-dudes were tightly backed by drummer Jon Theodore, bassist Juan Alderete and organist Isaiah Owens. Suffice it to say, when the combo rocked, they rocked; the soaring melody of "Roulette Dares" was intense and passionate and "This Apparatus Must Be Unearthed" -- the closest thing to a single on the band's new De- loused in the Comatorium -- was sadistic and snappy.

The shortfall, however, came in The Mars Volta's frequent lack of rock. Comatorium ventures well into the land of expansive prog, with many songs swelling beyond the eight-minute mark due to odd instrumental samples and stretches of freeform drone. On CD, the effect is intriguing, even soothing. In concert, it was utterly frustrating.

For one thing, the onstage improv was often reduced to pointless noodling. Rodriguez and Alderete fixated on what kinds of neato noises they could coax out of their digital delay pedals, regardless of whether or not the noises jived with the cadence of the song at hand. More distressing was Owens, whose planned contributions added a bebop feel to the punk chaos, but who simply banged on the keys randomly during the off-the-cuff moments. (Never mind Theodore, who disappeared for minutes at a time on more than one occasion.)

A bit of wanky jamming might have been tolerable were it just that: a bit. But while Comatorium clocks in at around 59 minutes, TMV played for well over an hour and a half with no break. Counting 2002's 20-minute Tremulant EP, the band's total catalog to date comes to 79 minutes, and they most certainly didn't play every song. Rather, half of the cuts in the set list were selected for embellishment, often doubling or tripling their length. The set-closing "Take the Veil Cerpin Taxt," a concise nine minutes on the album, approached a half-hour on stage, replete with nonsensical interjections by Bixler ("I am the stinger. I will sting you.") and a five-minute-long bass solo. Jams drifted so far from their origin that by the time the main riff/verse/chorus kicked back in, the initial reaction of the crowd was, "Hey, didn't we already hear this song?" before realizing that the song in fact never stopped.

Compare this with last summer, when Sparta -- ATDI's other half, featuring singer/guitarist Jim Ward, guitarist Paul Hinojos and drummer Tony Hajjar -- played the same venue. Fresh off the release of their Dreamworks debut, Wiretap Scars, the band plowed through the uppity Sunny Day-esque howling of "Air" and the radiant psychedelics of "Collapse." Songs were swift and tight, flowing without distractions or side trips, but something again seemed off. This time, it was Ward -- even when wailing, "Someday low notes fade away and go true and stale," in the bombastic chorus of "Sans Cosm," he just stayed put in front of his microphone stand. No presence, no animation, nothing but the music.

What the two camps brought to At the Drive-In during its existence was integral. The Mars Volta team gave the band a sense of fervor and immediacy desperately lacking from the Sparta team. However, Jim, Paul and Tony possessed a keen skill for song structure and constraints to keep the lofty experimentalism of Cedric and Omar in check. Conversely, the latter's homicidal leanings were tempered by the former's reserved stances while the former's less adventurous song structures were beefed up by the latter's ambition.

At the Drive-In was a beautiful balancing act in its day, and what happened to it was likely less of a need for time apart and more of the balance coming undone. It seems the two sides ultimately repelled one another into the territory of opposite extremity and, sweet as it would be, a reunion at this point is just a pipe dream.