Sounds interesting. Combat would have to be the focus of the game though (as following the greater theme of the movies) and you might want to have a pregen for combat strikes to the neck for that 'just right' kill. I'm assuming the Dark Quickening is based on the role of the Guardian in The Source movie. As I understand the movie and Guardian he was the test and only a pure good person could truly overcome the temptation not to take his head. Maybe a resistance / saving throw to determine if they can resist from taking the Guardian's head instead of fighting themselves.
I would also be cautious about giving the characters every single power of the deceased (feats, abilities, etc). You might want to give bonuses to similar skills of the deceased and victor, increased HP or magic power (if you use this), or similar enhancements.