A little more about a well-developed story than FPS gameplay.
Which brings me to my next point: Since you have these supernatural powers, but nobody else does, this game ends up being fairly easy to get through. Half the kills in it you can perform from the safety of around a corner by sending your "Creeping Dark" to do the killing for you. You really have the upper hand in almost every single confrontation, and it leaves a lot of the fight scenes a little unfulfilling. But does that really take away from this being a game worth playing? I don't really think so, just so long as you go into it looking for a very interesting storyline instead of a lot of shooting.
Basically, I see this game as being part Bioshock and part Chronicles of Riddick: Escape from Butcher Bay... and then that combination sold its soul to the devil. It has the same kind of action/adventure feel that Riddick did, where you could do side missions for other people in the game, outside of the actual story. Then, like in Bioshock, you had access to both your traditional guns and "other" weapons. Just instead of being genetically altered, you're possessed... By the way, parents, don't let your kids play this game.