My uncle put it beautifully when he said that he went into this movie not knowing who any of these main characters were. But when he left the movie caring so much for them and their stories.
Personally, I've become attached to these character just from the trailers, and I can't imagine how much more I will come to care for them when I eventually do go to see the movie.
I've ALWAYS been a backstory geek, whenever there's a backstory to any story or character that I like I'm all over any tid bit of their past I can get my hands on. And this story of Rogue One is backstory to not just pontentially episode IV but also the newest film in this Star Wars saga. Who knows what unexpected twists and turns in this Star Wars story may eventaully pay off in next year's upcoming episode VIII!
Until later, may the Force be with you!