I had this conversation/argument with my mother and cannot repeat the content of it here for fear of spoiling the film for you, but it basically concerned the realism of the story, an element which was obviously never part of the plan, or was but was then taken out. This does not cater to those who don't take any superhero or fantasy story seriously because it concerns made-up fantastical elements (people flying, aliens, superhuman powers, etc.) Those people simply can't think outside of the box and miss the whole point of fiction. This concerned the point that if you are going to put forth said fantastical elements, you have to explain logically how these elements react to and are effected by the world as we know it.
Sometimes, all it takes is a simple explanation. Ex: Peter Parker was bit by a radioactive spider. We don't know what would really happen to someone who was bit by one (we don't know what's in the radiation), and it's safe to assume they won't get powers if they were bit, but that area of reality is vague and uncertain enough for writers to fill it with their own mythology. The point is, he was bit by a radioactive spider, and his biologics reacted through giving him the abilities of a spider and that explains why he has his powers. You'd be hard-pressed to find this simple explanation in "Hancock". You be hard-pressed to find an explanation period.
In spite of the film having CGI the quality of which me and The Disturbed One could've simply made with Adobe Photoshop and HTML, besides certain scenes being rushed and ruined in the process, besides having a temporary villain that was completely worthless to the film as a whole (the film really focused on the three main characters.....or tried to anyway), it was fun watching Will Smith's character Hancock. He had a certain charm in the constant scrunching up of his mouth, his complete sloppiness and alcoholism, and his interaction with Ray Embrey (played by Jason Bateman) and sometimes with Mary Embrey (Charlize Theron). But this is about all I can say for what good elements the film had.