It's cool, the charge attack feels good to use, and dealing huge damage when damage boosting it is pretty satisfying. I like the designs (even though the inspiration is a little on the nose), and the animations are pretty nice, especially the arm animation on the first boss.
My biggest complaint would be the controls can feel a bit clunky, the jump not going as high when standing still threw me off a lot, you have to stand still to soul siphon, and a lot of your actions are just slow to start and end.
It's not bad though, nice job :)