Any ideas how to spice this up some more?

This sounds very good so far. Definately had a mood started. Dark and brooding. Nice. I would suggest the spice you might need would be a melody line to accent the main idea. Like some higher register sounds. Maybe some more orchestral percussion or possible really ugly sounding piano.

Think obscure sounds. Unconventional things that you can layer underneath everything, just to give it that push or something different.

Good LUCK!!!