Summerteeth sold far less than the albums Wilco made before and after it — but it holds up as the perfect entry point to what many people believe is America’s best rock band.

“The ashtray says you were up all night.” — “A Shot in the Arm”

Lines like that one hooked me on Wilco from the get-go. I’d seen band leader Jeff Tweedy workshop some of the group’s first two albums during solo and acoustic shows at his wife Sue’s (now long-defunct) legendary Chicago alt rock club Lounge Ax. But when I unwrapped their third record, Summerteeth, in the spring of 1999, I got a jolt like the one I imagine Beatles fans got with Sgt. Pepper’s.

Remember how Radiohead were a cool, mopey guitar band and then on their third album, OK Computer, they emerged from a sonic chrysalis with digital moves we never imagined? That’s Wilco’s Summerteeth, where they went from being a very good alt-country/power pop outfit to using the studio as a sonic playground and invisible fifth member.

Most people will tell you that Wilco’s 2002 album, Yankee Hotel Foxtrot—whose difficult birth was chronicled in the excellent documentary I Am Trying to Break Your Heart—was the leap forward that really pushed the band into uncharted territory. But because we consider it our job at Trunkworthy to make sure you have all the information you need to be a true Wilco-phile, we’re here to tell you that Summerteeth is truly the moment when Wilco became, well, Wilco.

Exploding like an everlasting gobstopper of new sounds, the album sprints from the first notes of the opener, “Can’t Stand It,” a song that chimes and soars, wheezes and boogies through a thicket of bells, sneaky pianos and majestic organ. “No love’s as random as my love/I can’t stand it,” Tweedy yelps on the chorus, not long after saying the very same thing about God’s love.

Tweedy mixes autobiography and dark fantasy on songs such as “She’s a Jar” and “I’m Always In Love.” His Henry Miller-esque lyrics about love and violence were written while missing his wife and first-born desperately as he worked on the album at Willie Nelson’s Texas studio.

“A Shot in the Arm” is the centerpiece of the album, with lyrical images so evocative they still haunt 15 years later. Tweedy talks about falling in love “in the key of C” and a lover who follows him down “the neck to D,” and how “what you once were isn’t what you want to be anymore.” With that setup line, he then rolls out the phrase that still confuses, and excites, to this day. “Something in my veins/bloodier than blood.”

It sounds like nonsense at first. What could be bloodier than blood? But that’s the point, right? A feeling so deep, so real, so visceral it defies rational description.

Wilco and British singer/songwriter Billy Bragg released the first edition of their Mermaid Avenue project in 1998, in which they wrote arrangements for previously unheard lyrics written by folk icon Woody Guthrie. And you can hear the influence all over the heartbreaking, creaking “Via Chicago,” which is so full of Woody-like phrases it reads like a mash note.

“Buried you alive in a fireworks display/Raining down on me,” Tweedy sings, his voice ragged over a subtle acoustic strum, funereal drum and spooky organ. “Your cold, hot blood ran away from me to the sea.” The wife couldn’t have felt great about the apology/threat in “ELT,” either, in which Tweedy admits he should have been listening to everything she said. “Oh, what have I been missing/Wishing, wishing that you were dead/I didn’t mean to be so disturbing/So far from home.”

If you’ve ever had one of those conversations while on a business trip—whether you’re a rock star or a medical equipment salesman—you’ve been there and Tweedy has written your anthem.

In the years since, Wilco has taken us down a series of odd paths. But Summerteeth remains the center of their kaleidoscopic world: an album where all the new and old parts come together in a jittery portrait of a true love that feels so good and so bad it hurts (and it feels like a kiss).