For a festival that too often gets criticized for its predictability, Summerfest certainly surprised with its booking of No Doubt -- the initial shocker being that a pop-ska band from the early '90s could fill the Marcus Amphitheater, and the second being that, wait! No Doubt is still a thing?

Tonight's performance proved that yes, No Doubt is still a thing; a very vivacious and animated thing totally hungry and ready to rip its claws into the spotlight again. Perhaps that's what a five-year hiatus does to a band.

Of course, frontwoman Gwen Stefani was about as far from on hiatus as a human being can be, launching herself into superstardom with her solo career, fashion label (LAMB), marriage to the hunky British guy from Bush and, of course, killer abs (which made an extended appearance tonight).

But if there was any inter-band resentment following Stefani's solo success, it was kept well under wraps or has completely dissipated as the four original members -- Stefani, bassist Tony Kanal, drummer Adrian Young and guitarist Tom Dumont -- were accompanied by friends Stephen Bradley and Gabrial McNair on their first tour since 2004. They appeared happy, playful and most of all, genuinely excited to be playing music together again.

The amphitheater lights went dark, a gigantic white sheet dropped and spotlights slowly rose to reveal four shadowed silhouettes as intro music built momentum. The tension reached its crescendo thanks to shrieks from the mostly-full venue and the band dove mightily into "Spiderwebs," the 1996 mega-hit. The crowed erupted into a bobbling mass, trying hard to imitate Stefani's sporadic skank outbursts (some succeeded, others looked like they were doing some kind of awkward Irish jig).

It followed up with the very Pharrell Willaims-influenced "Hella Good," and at one point Stefani had the bulk of her audience jumping on command and participating in rave-like calls and responses.

No Doubt was absolutely killing it after all these years.

It wasn't until after a few more favorites like "Underneath it All" -- with Stefani doing Lady Saw's rap part -- and "Ex Girlfriend" that the band slowed it down a bit to get some of the less commercially appreciated stuff out of the way, but it kept us thoroughly entertained with its videos, which played on giant screens behind the stage.

No Doubt is good to its fans. The show was a multi-media extravaganza with more energy than it could contain. The stage was cast in immaculate ivory with a large ramp that ran its length and hosted intermittent dance offs from the various members. And Stefani proved to be a total sweetheart, calling numerous fans up on stage, hugging them, snapping photos with them and acknowledging their homemade signs.

I was not privy to this special promotion, but word in the blogosphere said that people seated in top-tier sections on this tour received a free download of the band's entire music catalogue. It's a generous gift to be sure, but wouldn't you suppose that those willing to pay close to $80 a piece most likely already own most, if not all, of No Doubt's discography -- probably in multiple formats? Perhaps a better gift would have been a download coupon for the band's forthcoming record -- the first LP since 2001's "Rock Steady?" But, who are we to be greedy?

The band made no mention of the new studio work, and instead chose to forge back in time and rehash the greats from the past. Stefani called the reunion tour "the time of their lives," a statement backed up by a touching version of "Running" while a song's worth of old tour footage from the last decade played in a montage.

They closed the pre-encore set with 1995's breakthrough single, "Just a Girl," during which Stefani requested all the "Wisconsin boys" sing along. The band recently asked fans to submit their own versions of the video, which they'd hoped to show while on this tour. For whatever technical reason, they're unable to broadcast the homemade footage live, but you can catch an entertaining montage of the submissions here.

For an actual account of the song as No Doubt played it tonight, see the video clip below.