Great first half, ruined by second half

Rating: 5/10 (22 January 2016)

(Will warn when I get to the spoilers...)
The concept is superb: A superhero who acts like a bum and causes just as much damage as he does good, making the whole world hate him, yet he feels compelled to continue saving lives. What's more, Will Smith gives this character depth in a superb acting job, instead of just making him a cartoon character.
The first half sets up this character with just the right amount of comedy, and has him meet a PR guy who wants to help him improve his public image and himself as a person, leading to some great comedy.
(Major spoilers follow)
Then comes the second half that ruins everything. It's not that the second half switches into a different movie. It's that the writers seemed to have been drinking all of the bottles that Hancock left behind, and stopped making any sense whatsoever.
First of all, if he was a superhero for 3000 years before they found him in a hospital, then obviously the world knows who he is, so why did no one know him and tell him who he was?! And why would he and his doctors think he became a superhero only after his hospital stay? I don't believe they missed this obvious point. This alone kills the whole setup.
Second, if they become mortal every time he gets close to her, why didn't he feel anything during their first long family dinner together? Or worse: When they fought, why didn't they kill each other or cause any damage to each other? According to the ending, all he has to do is put a mere kilometer of distance between them to become immortal again, so obviously it's the distance alone that causes it, contradicting everything that happened before.
And what's the deal with the popcorn and tornadoes? Anyone? They get a triple-tornado when they get together and yet they stayed together several times before according to her, and the world didn't notice?
And then there's her character. It's like they used a different writer for each segment of the movie. She transitions from normal person to super-bitch, to crazy person who enjoys wrecking the city for no reason, who then claims to be stronger than him just for the feminists in the crowd (and yet the world forgot everything she did for 3000 years?), and finally to a self-sacrificing saint. I kept praying that the movie would switch back to the Hancock character and save itself, but it never did.
Huge disappointment. If only they had focused exclusively on his slower transition as a character...