Insidia Good, but can be better.
Actually, I'm quite confused by the theme. We are in a dark planet, that's OK. Spinning fans? Oh, science fiction. Demons/dark souls? Fantasy.
I just don't find mixed concepts interesting. OR if you want to mix them, let the player choose whom to side with, the technology or the nature.
Apart from that, very nice game. Of course the difficulty of a game shouldn't be too low but making it painfully hard is not good either. For the difficulty rating, I find it to my liking.
For a simple design, music is simple too. And it fits in the atmosphere flawlessly.
So I give an 8.
Arcane Castle