Isn't it awesome? And nobody had any idea in 1985. It looked like just another silly teen-centric comedy. Interesting to ponder why it turned out to be so enduring.
A combination of factors in my opinion. The casting was absolutely spot-on - from Michael J Fox's sometimes accident prone but quick-witted and brave Marty McFly, to Lloyd's zany and eccentric Doc Brown, to Thomas Wilson's loudmouthed and arrogant bully Biff Tannen. And they were all very, very likeable as characters. Even Biff - the villain of the piece - is unlikeable in a
likeable way - he's fun and amusing to watch on screen.
Then there's the car. It's different, unique and memorable - imagine if they had used some ordinary saloon? It's an iconic symbol for the franchise and is to Back to the Future, what the Millenium Falcon is to
Star Wars.
Then there's the soundtrack, the gadgets, the fashion in past, present and future, the backstory (no pun intended) showing how the lives of fringe characters like Goldie Wilson progressed. It builds a universe around them.
Ultimately though, I think the greatest strength of the franchise was how it's plot allowed them to straddle timelines and effectively give us 4 different types of film in one franchise. You had the contemporary 80s bits; the throwback to 1955, the almost sci-fi future Hill Valley of 2015, and then the 1880s Western era. It was a lot of bang for buck.
The film just combined these elements in the right way, at the right time. Had they come out in the 90s, or kept Eric Stoltz as the lead, or done a number of other things different, they may not have had the same cultural impact.