To put it as charitably as possible: I have, uh, mixed feelings about the Grateful Dead. It turns out Jerry Garcia did, too, and the final stretches of Long Strange Trip—Amazon’s four-hour documentary covering the 30-year career of the starter-yeast of all jam bands—examine the guitarist’s difficulty with his role in the most successful cult band in history.

Garcia’s decline and death make for a moving conclusion to director Amir Bar-Lev’s film, but like the Grateful Dead’s live shows, you’ll have to sift through dead ends, hazily presented thoughts, and some flat-out bad music to get to the good parts.

Still, no matter how you feel about their songs, the Grateful Dead’s story is a fascinating one, and not solely because of all the drugs involved. The Dead were signposts for two crucial transitions in the American underground: when the beatniks gave way to the hippies, and then when hippie culture became big business.

Jack Kerouac and Ken Kesey influenced the Grateful Dead as much as any musician, and the group’s dedication to live improvisation—applying the philosophy of jazz to a rock ’n’ roll medium—never wavered, even when they amassed stadium-sized crowds.

Long Strange Trip may be a challenging proposition for non-devotees, but it’s worth diving into if you have even a mild interest in 20th-century music or American history. Deadheads will eat it up, of course—and take issue with parts of it, as the movie is unflinching in addressing how the band left noticeable casualties in the wake of their success.

Most of the band interviews are garbled gobbledygook (oh, Bob Weir, you bearded panda of nonsense), but the most insightful moments come from grizzled British tour manager Sam Cutler and honey-bear roadie Steve Parish. Long Strange Trip is an acid-dipped love letter that doesn’t pull any punches.