Marty hangs out with Lloyd once too often, and ends up accidentally transported to 1955 (30 years prior) in Lloyd's time machine DeLorean automobile. But it has used up its plutonium, and it appears that Fox is trapped in 1955. Worse, he encounters his future parents, Glover and Thompson, and unwittingly interferes with their romance, which jeopardizes Fox's own existence. Fortunately, Lloyd is also in 1955, and helps Fox set things right again.
How others will see it. A box office bonanza, Back to the Future spawned two sequels and a Saturday morning television series. Critical praise was enthusive, although its status of a mainstream comedy precluded Oscar glory. Among the major categories, it was nominated only for Best Screenplay. The Golden Globes nominated it for Best Comedy (losing to the mostly forgotten Prizzi's Honor), while BAFTA gave it a nod for Best Film (losing to a well-received but little-seen Woody Allen movie).
Three decades later, Back to the Future remains beloved. At imdb.com, it has a lofty 8.5 user rating and a humongous 700K user votes. There is a modest decline in grades with advancing age of the viewer, from 8.8 under 18 to 8.2 over 45, ironic since younger viewers don't remember either 1955 or 1985. The user reviews are virtually unanimously positive, save for a few pouts over bad science fiction, as demonstrated by my own comments below.
How I felt about it. The entire concept of interactive time travel is absurd. For example, the moment that Marty prevents George from getting hit by Lorraine's dad's car, Marty should no longer exist. Even if George and Lorraine should later become married, the new "leader among men" George McFly is so different from the dweeb George McFly that the kids would be born and raised under different circumstances. There would be a Marty, assuming that a boy was among Lorraine's three children, but he would be genetically different.
But since the Marty we know was never born, he could not return to 1955 to interfere with history. Thus, the car would hit George, Lorraine would fall in love with him, and Marty would exist. The obvious solution to the conundrum is that Marty cannot go back in time. Or anyone else, either.
We won't even bother to guess the odds that the DeLorean would reach 88 miles per hour, on the short streets of Hill Valley, and connect with a wire at the same fraction of a second that the wire is electrified by a lightning strike. Actually, Marty should have been shot dead several times over by the Libyans before he even reached 1955.
Plot holes aside (and there are many), the movie can be enjoyed strictly as a comedy. It is a marvel of casting. All the consequential actors are delightful in their roles, down to the curmudgeon who owns the local diner. The script is endlessly amusing, especially after you have seen the movie a few times, and can pick up on the full import of lines like "history is gonna change."
As blockbusters comedies go, the movie is more than a standout, it is a marvel. Zemeckis' active direction, Spielberg's detail-oriented production, and the clever Zemeckis/Bob Gale script fit like a glove. They had previously all worked together on I Want to Hold Your Hand (1978), 1941 (1979), and Used Cars (1980), although I can only recommend the first of those three movies.