There is a good chance someone you love or admire has what you consider an inexplicable passion for the noodling, formless hippie rock of the Grateful Dead. That person—frequently, me—may continue to hector you: just listen to this one song from the ‘72 show in London! Even just the studio version of “Casey Jones!” I know: we’re annoying.

But now, this decades-long battle of musical trench warfare may finally be over. If a Dead-averse individual sits down and watches, really watches Amir Bar-Lev’s documentary Long Strange Trip and doesn’t emerge with an “O.K., O.K., I get it,” it’s officially time to give up on them. Then again, as one superfan explains in this film, most don’t become Deadheads without some sort of mentor. So let the cryptical envelopment begin.

Long Strange Trip, which boasts Martin Scorsese as an executive producer, is four hours long, and was shown with a 10-minute “set-break” at its Sundance debut. (It will be available to stream via Amazon in May. It is currently unclear whether there will be a concurrent, brief theatrical release in select cities.) The length may sound excessive, but this is the band that, more than any other, brought jazz-influenced, sometimes 30-minute-long improvisations into the rock world.

The film’s first half is a typical, though very well-polished rock doc: getting the band together, how they found their sound, their struggles and successes. After intermission, the narrative goes to unexpected and extremely emotional places: an examination of intense public adoration and the burdens of fame. For lack of a better term, it becomes a real movie.

Bar-Lev actually structures the film like one of the Dead’s legendary performances. (They toured pretty much nonstop from their formation in the late 1960s through 1995.) Typically, their first set would feature shorter, sing-along tunes, and the second set would be a psychedelic exploration beyond time and thought, the primordial “Rhythm Devils” double percussion ceremony (also called simply “Drums”) segueing into the atonal free-playing of “Space.” Eventually, the band would float back to Earth with one of Jerry Garcia’s tender ballads, galvanized by his lightning bolt electric guitar.

Oh my God, I am this far into telling you about this movie and I haven’t even mentioned Jerry Garcia yet! Now you can see why it lasts four hours. Garcia, the bluegrass banjo player who loved Beat poetry and LSD., was always the musical leader of the group, but really fell into the role of front-man after keyboardist and R&B-inspired vocalist Pigpen (a.k.a. Ron McKernan) died in 1973.

The Dead were already a counter-culture staple, perhaps the most beloved band of the Haight-Ashbury scene in San Fransisco. (Being the unofficial house band at Ken Kesey’s “Acid Test” parties helped them land that position.) But when Garcia took the spotlight, with baritone singer and unconventional rhythm guitarist Bob Weir as his wingman, that’s when everything truly snapped into place.

What made the Dead different is what’s foremost on Bar-Lev’s mind, to the point where a lot of expected moments are missing from the film. You won’t learn why Garcia is missing a finger. The word “Woodstock” (where the Dead performed) isn’t mentioned once. All of the band members’ solo recordings, many of which made it into the main repertoire, go undiscussed.

But that’s O.K. It’s all on Wikipedia. Instead, we go deep on the group’s unusual ingredients. Long Strange Trip serves as a fine history of LSD, a substance innately interlaced with the group. (At one point, we see footage from a canceled movie project—canceled because the band kept slipping the film crew acid, and the resulting material was incoherent.) Similarly, there’s a substantial sequence discussing the history of concert amplification systems. In a nice blending of these two topics, it was the famous LSD chemist Owsley Stanley, the sorcerer behind what was alleged to be the best acid ever cooked, who, using his drug money, devised the Dead’s notorious audio rig called the Wall of Sound.