First: I'm new..and I'm German...so please have mercy ;)
It's strange: I'm really looking forward to this game. I waited for this since a was a kid and even tried my own attemd to design and program a Bttf adventure. Because of that, I have some fears that I will be disappointed. But I also know that TTG has great expertise and they just make very cool games, so I'm confident again ;)
So here are my personl thoughts about what makes Bttf so unique and outstanding from other Time traveling movies and what would be great to be considered in game/story design. And even more: What I DON'T think a Bttf game should include.
1. Accidantially lost in time and messing it up
A great deal in the first movie is the whole concept of stranded in time and just messing it all up. In this terms, Marty is similar to Guybrush in Monkey 2, both are anti-heros. Marty changes time by jumping in front of his grandpas car and now has messed everything up. Guybrush shows Largo the beard of LeChuck, which results in LeChuck being reborn (well, kind of). So the whole story is about fixing things, that the main character messed up. This is pure fun and it's very personal and stays in the family!
I don't want the story to be around typical time traveling issues. There is a desaster coming, a world war, a nuclear explosion oder something like that, so Marty has to jump to that time and prevent something terrible from happening. That ain't fun, it's a "Time travel police" thing. I don't want that. We have that covered this weak time traveling movies enough.
2. Just a few unique characters, in different timelines
Huge fun is also watching the same characters in different timelines. This was a bit weak in the last movie, because there were just ancestors of the real characters and not the characters themselves.
So please include all the main characters again, feel free to add some unique characters at well, but let's see them in different timelines. Visit a grandpa of your enemy and tell him a story he then tells his grandson, which effects the present etc.
Have several characters, that have nothing to contribute to the story. When you have a close look at the movies, there aren't many 'NPCs' there, that are just there to talk a few lines. They are often really unique and funny.
3. Fun, but not comedy
The fun of Bttf results in the situation, which are unfamiliar...your mom beeing into you and wants to kiss you is something that maybe can't be topped.
Don't use this Monkey Island / Sam 'n' Max humor on that. It just doesn't fit. It should have a fair about of serious athmosphere but with surreal and timed humor in certain situations.
That's it for know. I think, I have a lot more feelings about that, but can't express them right. Overall, it's all about rescuing your family and fix the things you messed up by your own. While fixing that, you mess up something else etc. I think, these are the essentials of Bttf.
What do you think?