You should know you have problems when the moral centre of your story is a PR executive.
Indeed it's not hard to see why this script floated around Hollywood for a decade before finding a willing producer. One of its main premises has a great deal of potential, but there are also quite a few built-in flaws, which would have been very apparent to any backer...right up to the moment when Will Smith stepped up to take the lead!
Hancock's problem is ultimately a lack of decent antagonists. Having seen off his own asshole self in the promising satirical-comedy opening, the rest of the film sees him not really confronting his former other half and not really confronting a non-descript gang of roughneck crims. Along the way the writers lost the will to be funny, yet in spite of its rather half-baked halves, Hancock does, just about, manage to remain an entertaining way to spend an evening.