Back to the Future is absolutely the best movie ever made. It's part of my childhood, it's about time travel, it's funny, it's a GREAT story, it's well acted and it hits all of the other happy buttons in my brain.
This movie made the DeLorean a cultural icon. It wasn't a very good car (as far as I'm aware), but 35+ years after the movie I think it has a good chance of being an entire generation's mid-life crisis purchase.
Christopher Lloyd is a gem. He was the perfect role for this movie and the way he played it was pitch perfect. Him and Michael J. Fox are wonderful together and have great screen chemistry.
Time travel movies are difficult for exposition... There's often a lot of information that needs to be brain dumped to the audience so they understand the mechanics or whatever else. The writing in this movie does that expertly. The conversation the McFly's have over dinner about how Lorraine and George met, for instance. It sets up the paradox Marty creates and the Enchantment Under the Sea story ties nicely into the finale.