The Darkness is a FPS from Starbreeze, the developers of Chronicles of Riddick. In the game you play as Jackie Estacado. On the night of his twenty-first birthday, Jackie finds out he's being possesed by a demon called The Darkness. Manifesting as two demon snakes sprouting out of his shoulders, The Darkness helps Jackie out in taking revenge on his Uncle Paulie, who has wronged Jackie, and at the same time attempts to manipulate him. And you eat hearts from fallen enemies in this game. It's awesome.
The Darkness has a very compelling story, with interesting characters that are voiced really well by the voice-cast.

Graphics are great, the New York setting is very recognizable, and the "WWI in hell"(you heard me) is also very good. The characters look quite lifelike and the ragdoll when you use your Darkness Powers, which I'll get to later, is impressive. It's a very goodlooking game overall.
The gunplay in The Darkness feels somewhat weak, and your pistols are pretty much the best guns in the game. Making dual pistols more effective than a shotgun, even when shooting an enemie from upclose, is lame. The weak gunplay is more than made up for by the Darkness Powers. You get Creeping Dark early on, which allows you to send out one of the snakes on your shoulders to sneak around, even on walls and ceilings, breaking vents

The Darkness can be compared with games like Bioshock, that have it's atmosphere as a main selling point. I'd say if you liked Bioshock, you'll The Darkness. It's not terribly long, but it's a fantastic experience.