Just the other day I mentioned how part of the uniqueness of Christopher Nolan's Dark Knight is the way that he spins fantasy in a way that makes it seem potential real and rather than "comical" something deeply psychological.
Similarly, I think that is were the David Fincher's film The Curious Case of Benjamin Button is most successful. (warning post may contain minor spoilers).
The story is clearly not based on a true story or anything close, it's completely fantastical...no spoiler there. The story of a man who ages is backwards is beyond the diagnostic abilities of Dr. House.
Yet, at the same time...there are a number of moving parts in the film, and screenwriter Eric Roth has crafted the film in such a way that despite the fantastical elements, you can easily find yourself finding sympathy for Benjamin. Whether something's concrete like being abandoned by his father at birth, or something more theoretical like the challenges of loving someone who's life is going in a different direction then your own, I believe many people find themselves emotionally connected to Benjamin Button.
One of the curious decisions that I found that Eric Roth made in this film was the way in which he had the story narrated by a dying Daisy who's daughter reads from Benjamin journal...at this same time Hurricane Katrina is headed towards Daisy's New Orleans hospital.
Certainly, F. Scott Fitzgerald in his original creation of this story did not have any intentions of including this type of plot detail, but I think placing real events, places, and cultural history in the film helped detach viewers from the fantasy and send them into a world of reality.
By placing years, and time on the events it let's viewers experience basic human emotions, thoughts, and feelings in a fresh way. In many ways this film offers the same appeal as Forrest Gump in that regards. The characters might be so unique that there rather common personal discoveries seem fresh, catching viewers off guard.
To me, this is the real magic of The Curious Case of Benjamin Button.