It's been years since I've seen Back to the Future 2, but it was my favorite when I was a kid. It's easily the best sequel that was essentially a retread of the original. I don't care about the flying cars so much as I'm sorely disappointed we don't have Mr. Fusions.
Here's the link. From the article:
One thing that we absolutely missed completely was cellphones and smartphones. We didn’t figure that one out at all. If you were going to say, what would Doc Brown be surprised by if he actually got to 2015, that would probably be it. This is a technology that nobody saw coming in 1989, and it’s totally ubiquitous now and has totally changed how people live.