There are myriad lessons that one can take away from a weekend at Bonnaroo. Walking the gargantuan Tennessee festival for four days in June is a physically humbling endeavor; a lot of people who pony up for the ticket don’t necessarily possess the explorer’s spirit required to get the most out of what they’re given; there is no such thing as a fourth wall when it comes to live music; there are in fact a lot of people with $25,000 to blow for the ultra VIP experience; and at Bonnaroo, one should always expect the unexpected.

Then there is wisdom bestowed from the performers themselves. Among the pithiest of them all came from the mumbling Bad Brains frontman HR, who captained a rare set by the DC hardcore legends’ Saturday afternoon set clad like Leon Russell, with blonde wig, white suit and hat, and feather boa. Just minutes into their set, moshers, skankers and crowd surfers were worked into a violent lather by a vicious opening salvo of Rock for Light staples “Attitude” and “Right Brigade.” They had kicked up a choking dust storm, bodies were flying over the front railing, photographers were fleeing the pit and the aging aggro-farians were tossing gas on the fire. But the moment that guitarist Dr. Know pushed “Sailin’ On” to a breakneck crescendo, all that rage melted away with a masterful transition from ferocious punk into Jah’s own dub, like a needed dose of sonic Prozac for a group of people trying to kill each other.

“The lesson for today is, ‘Courtesy is contagious,’” HR declared at its conclusion as the audience exploded with applause and cheers.

HR was a goldmine of bemused soundbites whenever he spoke intelligibly into the mic, usually addressing the crowd with “boys and girls” like Bill Cosby on a Mortimer Ichabod Marker interstitial. “This next song is… a masterpiece,” he said as an introduction to the blissed “I & I Survive,” a groovy prelude to mashers “Pay to Cum,” “Re-Ignition,” and a stoner-metal closer simply noted on the set list as “New Joint.” Flea of the Red Hot Chili Peppers approved.

Photographers had less to fear from the hail of limbs at Bad Brains’ mostly roiling set than they did later at the same spot from the dark prince himself, as Danzig bolted from the middle of “Skulls” during a career retrospective to personally enforce his own “no photo” policy. Apparently not privy to the teachings of HR earlier, Danzig had made it all the way out to the edge of That Tent to muscle down on a guy taking crowd shots before being stopped by security (who graciously let him return to the stage with his own dome intact).

That Tent was the de facto home of metal for the weekend, hosting an ambitious Alice Cooper performance during the late-night block, but was also the nerve center for the cult of personality that was especially strong at Bonnaroo’s 11th installment. In addition to Cooper, the weirdo HR and Danzig in classic jerk form, a set by Puscifer, Maynard James Keenan of Tool’s sexually charged experimental metal outfit, was something like comic relief to those truly committed to Saturday’s heavy lineup. The day after Keenan wandered through the What Stage pit for Radiohead’s set wearing reading glasses that paled Shelley Berman’s in size, he led his crew onstage dressed as a commercial flight crew, complete with beverage cart, boxes of bagged peanuts (which he shared) and an amply-proportioned flight attendant. Keenan’s Fred Flintstone tie was a nice touch, but stopping between songs to cut a lemon and pour himself a drink put the surrealist element over the top.

But then, it wouldn’t be Bonnaroo if every happening was readily believable, or even conventional for that matter. Those who packed into Saturday night’s Superjam just after midnight witnessed something similarly historical. Questlove of the Roots, who had just dedicated their own set to the dear-departed Adam Yauch of the Beastie Boys and go-go godfather Chuck Brown, reminded the crowd that he was given carte blanche to put together something amazing. Wouldn’t you know it, he delivered.

Sitting behind his drum kit, Questlove announced the show’s lineup, Philly-based one and all. First came the Roots’ own Kirk Douglas, James Poyser and Frank Knuckles. Then Prince’s sax player Eric Leeds joined. Next came Pino Palladino — the bassist of record for the Who, Adele and Simon & Garfunkel — followed by Jesse Johnson, original guitarist for the Time. Then came one of those “Shit, damn, motherfucker” moments.

“I’ve been waiting 12 years to say this,” Questo said with one more name on his lips. “Ladies and gentlemen, D’Angelo.”

It had been that long since the reclusive neo-soul crooner had set foot on an American stage, but that streak was over. Taking the stage in a black do-rag and leather vest, holding an angular black Fender guitar and sitting down before a Rhodes piano, D’Angelo’s return to music was complete. And it was magnificent. The band blazed through the Ohio Players’ “Pride and Vanity,” Led Zeppelin’s “What Is and What Should Never Be,” Jimi Hendrix’s “Electric Ladyland” and “Power of Soul,” Prince’s “My Summertime Thang,” Funkadelic’s “Hit It and Quit It” and “Funky $ Bill,” the Beatles’ “She Came In Through the Bathroom Window” and the lone D’Angelo original “Go Back 2 That Thing.” D’Angelo isn’t quite back into Voodoo shape, but he’s been working on his guitar chops as much as he has his body, and James River might as well now be the most anticipated album of 2012.

Not much else could approach the level of awesome that came with witnessing D’Angelo’s return, but Kenny Rogers, of all people, made the most concerted effort on Sunday. The Antlers’ Peter Silberman could be heard from his stage voicing his own excitement to see the Gambler in person, and it was warranted. Rogers promised to play every hit he ever had, but what he didn’t promise was a special guest. Newly converted country star Lionel Richie ran onstage and shared a heartfelt duet on “Lady” before Richie brought out a show-stealing “All Night Long” while the squinty-eyed Rogers looked on. At Bonnaroo, the unexpected rules.

Bonna-bullets

■The difference between the Mike Love-led Beach Boys that toured last year and the completely reunited Beach Boys of today is remarkable. Love and Bruce Johnston’s group was serviceable, but the presence of Brian Wilson — however disconnected from everything he might appear — changes everything. For all the holes in their new album, something like “Isn’t It Time?” sounds sweet, simple and incredible when he sings it to you. There’s no questioning his genius, but seeing the disparity between two incarnations only amplifies it.

■I’ll never fire up Skrillex on the ol’ iPod, but his show looked fun from afar. Too bad it still sounded awful. Nonetheless, with a head full of the right stimulants, the steam blasts, lasers, and incessant woompwoompwoomp from starfighter-shaped DJ booth could have made for a pretty cool experience.

■Darondo’s canceled Saturday set was among the festival’s bigger disappointments, but it did open the door to see the incredible Janka Nabay & Bubu Gang. The Sierra Leonean singer blended dancehall, dub, Afrobeat and trippy electronica, backed by a crew of Brooklyn players borrowed from Gang Gang Dance and Starring. His first album on David Byrne’s Luaka Bop label is outstanding, and if more than a dozen people had seen his set, it might have easily been considered among the weekend’s best.

■Boy howdy, did This Tent pack the subwoofers in. The stage that hosted Ludacris and Major Lazer would have to out of necessity, but the thump that came from it was substantially more intense than anywhere else. You could feel Ludacris’s set — easily the most insanely packed tent show of the weekend — before hearing it. It made sense that this was the place where Fitz & the Tantrums had a terrific duo of sign language interpreters creating lusty, real-time interpretations of their bedroom-soul jam; the deaf can get as much enjoyment from the physical sensation of music as the hearing can conventionally.

■Thursday night at Bonnaroo has gone from being the place to really hit the up-and-coming gems to being more of a hassle than it’s worth. Tent shows are so packed with the stages closed that it’s hard to breathe, and you often find yourself waiting in one place all night to see one band up close. For me, that band was Alabama Shakes and wouldn’t you know it, hearing them live reveals them to be a little too hyped.

■It was hard to tell whether you were at the Bonnaroo main stage on a Friday evening waiting for Radiohead or in Vegas taking in an epic spectacle of a show by scintillating guitarists Rodrigo y Gabriela with the 13-piece orchestra CUBA. It felt bigger than anything Bonnaroo has ever done despite their pre-headliner status and was easily among the weekend’s standout sets.