Hancock is clearly a Superman-style superhero--super strong, invulnerable, flies, etc--but has, shall we say, "issues"...and if the movie is 1/4 as good as the preview makes it look, it's going to be a good one.
I'm sure the plot is pretty much a standard superhero movie plot. At least the concept has a few elements of uniqueness to it. I may have to see this one in the theater.