Simple Pleasures
I don't have a lot to add to what has already been said ... you've got a great concept here.
This particular comment is beating a dead horse BUT ... I feel it's very valid. If Cthulhu automatically has enough 'strength' in the mortal realm to mutate and brainwash folks, it would make a lot of sense that his powers would grow as the game wore on. I feel that perhaps every 3 levels he gets some new ability. Maybe an electrical shock that drains your charge bar AND damages enemies? Perhaps a power that boosts the speed of your power-bar for a period of time? Like someone suggested, give him the ability to create his own minions.
I enjoyed the game and hope you can make improvements in a sequal or even an update to this version.