The 2015 of "Back to the Future Part II" featured flying cars, hover boards, self-tieing sneakers and high-tech clothes. Here's how the movie compares to real life. (Jorge Ribas/The Washington Post)

Our density — or rather, our destiny — has brought us to this day.

It is finally Oct. 21, 2015, the same date that Doc Brown punches into the circuits of his time-traveling DeLorean in 1989’s “Back to the Future Part II,” thereby sending himself, Marty McFly and Marty’s girlfriend, Jennifer, into a future featuring flying cars (that prediction didn’t quite pan out), video conferencing (that, they actually got right), the Chicago Cubs as World Series champions (uh . . . possibly correct?) and an obsession with ’80s nostalgia (spot-on). That fiction-meets-reality connection has marked Wednesday as “Back to the Future” Day, a momentous movie-fandom occasion to be commemorated with screenings of the “Back to the Future” trilogy, in theaters and on television; the arrival of a documentary about the movies; the release of a new DVD and Blu-ray set; a new “Back to the Future” book, which comes on the heels of another book released this year; and, undoubtedly, a barrage of Twitter trends, Facebook shares and Instagram posts that will serve as testament to the love of flux capacitors that still fluxes so energetically in our hearts.

For “Back to the Future” purists, though, this moment may also serve as a frustrating reminder that the way we think of these movies has changed since the ’80s/early ’90s. Now prevailing sentiment — or perhaps, a narrative forced upon us by Universal Studios marketing — has persuaded us to regard “Back to the Future” as a single entity, a story whose three parts are each worthy of equal attention and celebration. The thing is: They’re not.

The original “Back to the Future” stands among the most entertaining and intelligent Hollywood blockbusters ever made, one that won over critics as well as moviegoers and became an enduring pop culture phenomenon. But it was followed by two decidedly inferior sequels — by no means the worst sequels ever made, but certainly time-travel adventures not nearly as good as the first. Yet because of DVD box sets that package the three together, marathon cable TV airings of all the “Back to the Futures,” and younger audiences who know the Marty McFly story only as a binge-watching experience, we have been trained to think of “Back to the Future” as a trilogy instead of what it is: a masterpiece followed by two lesser-thans. Placing so much emphasis on Parts II and III — but especially II — feels like a revision to the history of a movie that tells us exactly how dangerous it can be to go back and revise history. It’s as though the correct understanding of “Back to the Future” has been . . . [whispers in Doc Brown voice] . . . “erased from existence.”

1985’s heavy smash

“Back to the Future” did many things in 1985, the year it was released and became a sensation. It provided rocket fuel for Michael J. Fox’s already rising career, making us love him so much that we willingly spent good money to see him in the patently ridiculous “Teen Wolf.” It blended the two most revered genres of the decade — the sci-fi picture and the teen movie — with humor, zip and big, Frank Capraesque heart. It also became a massive moneymaker, staying parked at or near the top of the box office for five months and earning more than $210 million in North America alone, a colossal total at the time.

According to the book “Back to the Future: The Ultimate Visual History,” Sid Sheinberg, then head of Universal, told the film’s co-creators, writer-director Robert Zemeckis and co-writer Bob Gale, that a sequel would be made whether they were involved or not. So after making sure that Fox, Christopher Lloyd (who plays Doc) and some of the other key actors were onboard, the two Bobs did the best they could to craft another chapter. They came up with a “Part II,” which picks up where the first one left off, sending Marty (Fox) and Doc Brown 30 years into the future as well as back to 1955; they also conceptualized a “Part III,” which flings the pair to the Old West.

Most sequels operate on the principle that the audience wants to return to the world and characters they recognize from the first movie. “Back to the Future Part II” — the more memorable, problematic and relevant to “Back to the Future” Day of the two follow-ups — takes that idea as literally as it’s possible to take it. It opens with the same scene that closed the first film, shot-for-shot and beat-for-beat, but with one key difference: because Claudia Wells, the actress who originally played Marty’s girlfriend, was unavailable to do the movie, the character Jennifer is now Elisabeth Shue. From the get-go, it feels like someone traveled back in time, interfered with “Back to the Future” as we knew it and turned it into this: the same movie, but with the babysitter from “Adventures in Babysitting.”

The whole movie is like that. Marty’s father, George, is back, but replaced by an actor who clearly isn’t Crispin Glover, despite all the facial prosthetics that try to convince us otherwise. The skateboard chase scene from the first movie happens again, but in 2015, Marty’s on a hoverboard instead of a skateboard, attempting to avoid Biff’s grandson instead of Biff. A second Marty from the future, disguised in a fedora that makes him look like an aspiring Jack Abramoff, revisits the Enchantment Under the Sea dance in 1955, but this time he’s crawling across the lights above the stage where his other future self performs “Johnny B. Goode” the way he did in the original. It’s as though the entire film is saying, “You know that story you loved? Well, here’s a bunch of new details that will make you remember it completely differently.”

“Back to the Future Part II” changes our ability to look at “Back to the Future” the same way, just as Marty’s actions in the first “Back to the Future” change the past and future, too. That’s a brilliant concept that, in execution, feels really depressing. The worst thing a sequel can do is ruin the first one. “Back to the Future” is too great to be “ruined,” but Part II comes pretty close.

Many critics at the time agreed; Roger Ebert acknowledged that the movie was “fun,” but he also said it “lacks the genuine power of the original.” The Chicago Tribune’s Dave Kehr called it “glum, claustrophobic and often oppressive.”

Yet here we are on “Back to the Future” Day, celebrating that second film’s journey in a way that gives it as much significance as the first one. To those born after 1985, who grew up watching “Back to the Future” as a trilogy, that may feel perfectly appropriate. As someone who considers “Back to the Future” a movie that belongs to my generation — us old, overlooked Gen-Xers who grew up spellbound by the wonders conjured by Spielberg, Zemeckis and Lucas — it feels like something got lost.

It’s widely known that Eric Stoltz was originally cast as Marty in “Back to the Future” and eventually fired by Zemeckis and replaced with Fox, yet another detail about these films that taps into the notion of history being modified.

In that “Back to the Future” visual-history book, co-star Lea Thompson recounts something Stoltz said after the first table-read of the script: “It’s kinda sad, because Marty remembers the past, and everyone else he loves remembers a completely different past.”

That’s how it feels sometimes to love “Back to the Future.” Some of us recall a time when those four words referred solely to that original, wonderful, Great-Scott-gigawatt of a movie. But everyone else, it seems, thinks of something larger, less perfect and completely different.

Chaney is a freelance writer.