I'll have to agree with everything Fervir has already said:
* While you can get away with using bfxr (I am) you can't just settle on the first thing that comes out. Music may also mask it a bit better too.
* There wasn't a whole lot to do in the demo, but the potential variance in levels and enemies seems promising. Definitely work on the level generation, because some of the levels were very empty. Very much enjoyed the summoning/souls aspect.
* The lighting made the game look very very nice, but again the speed of the fireflies were too slow sometimes.
It definitely has potential. Keep at it!