I think your melody and harmony was really solid, well done! I think you could improve most in the drum department, a little less chaotic and a bit more steady (even though I loved some of the chaotic elements) would go a long way here. Also, some of the drum hits were not properly timed/quantized or accidentally "left over", which took me out of it sometimes.
I think Blue Lava has made some excellent points regarding instrumentation options. You can get a good understanding of what people conceive as Halloween-y by listening to the other entries and especially reading the comments.