The storyline is that Jackie Estacado, a known name in the New York mob business, is part of a long line of Estacados who were chosen by an evil entity known only as The Darkness to be its host. It is said that The Darkness could see into the future of the Estacado's bloodline and see the evil that would breed in their hearts, and The Darkness feeds off of that evil; that darkness.
The Darkness manifests in its hosts as soon as they hit their 21st birthday, and if they have sex and pass on their seed that host will instantly die and the Darkness will have to lay in wait in the new host until their 21st birthday. I'm not sure why it has to be 21, perhaps the Darkness wants its host to be of legal drinking age, who knows.
This game doesn't go into the history of this ancient evil until about the middle of the game, so the entire time you're playing before then you're wondering how it came to be, what makes it this way, and how you can defeat it so you can stop listening to Mike Patton's voice growling through your speakers (which is actually very cool, especially once you know that he did the voices without any special effects added.)
For fans of the comics, it will be a nice flash-back into the origins of the Darkness but it will also bring something new to the tale as it brings in some of the game elements as well.
