The game is very dark. You play as a crime lord's nephew who somehow becomes bound with a demon. In the demo, you get to summon these two snake-like shadow heads on your shoulders, and use them to, say, bite off an attacker's face, and then eat their heart. You also get a 'demon arm' which you can use to pick things up and impale enemies with. How you manifest this power is by:
-Having your snake things eat hearts -Absorbing the powers of the darkness
Obviously, shadow demons don't do so good in the light. Summoning your compadres in the light will give off a sizzling sound, and also begin draining your darkness power.
There are also places in the dark nooks and crannies of a level where you can summon minions. Berserkers have these sword things, I saw one jump on an enemy, impale him, then slice his neck with a rusty saw. Gunners are better suited for long range stuff, which is a duh, and Kamikaze minions don't even need an explanation.
The following gameplay videos are a walkthrough of sorts of the demo, enjoy, if you're not squeemish.(EDIT: These are actually recordings of the full game. The demo had segmented stages.)
(As a warning, this has bad language and lots of blood and stuff)
