I like the murky atmosphere at the beginning. Definitely feels Halloweeny. :)
The way the drums faded in sounded a bit bizarre. Fading them in with filtering as opposed to just volume might've been smoother. There's a bit of dissonance in the texture at around the 1-minute mark, and the transition at 1:19 is pretty sudden. The texture feels like it's missing a lot of mid-range frequencies. The complex rhythmic structure of the piece would also come through more clearly if the different harmonies weren't so close together in pitch.
I also feel like the song needs a more prominent lead riff. Right now, the echo-y mid-range bass riff that serves as the lead for most of the piece (it plays in isolation at 3:48) sounds a little too minimal and murky to really stand out.
Overall, not your best, but you definitely nailed the creepy mood and sound design. Happy belated Halloween! ^_^