Nice
Quite an interesting piece of work. I must say, when I read the description, I was expecting something pointing about 180 degrees in the opposite direction of what the song actually looks like, but it's an excellent song nonetheless. When you said epic, I was actually picturing something loaded with heavy strings and 4-octave chords, when you have actually gone for a somewhat softer synth background. Definitely not my idea of epic, but works like a charm for creating a tense atmosphere.
Also, I must point out that I don't really agree on this song being "aggressive". True, the bass-line you wrote has the potential to cause outbursts of rage against small furry animals, but definitely not with the pace of the drums that you have chosen. If we were talking about a rampaging drum section, I'd consider calling this aggressive. As far as boss battles go, this also seems to have a slightly too long build-up, as boss battle themes (from my point of view, at least) need to have more of an in-medias-res factor.
Now to the instruments: the sound of the bass was nice, and I love the way you used the muted notes to give it a bit more adrenaline, which also worked well with the sections where you let it get dissipated in the effects. The short synth leads you used are really nice for the progressions you used, and they seemed to create an icy feeling, especially when combined with the piano-esque sounds and strings. The drums could've been a tad louder, but I guess that's just a matter of personal preference.
Overall, I'd say that the songs over-repetitive bass-line gives the feeling of massive lack of diversity. Which is a shame, seeing that you obviously put a lot of effort into it: the volume control, effects and all. So: speeding up the drums and adding another bridge-section in the middle (just to break the monotony) is all I can actually suggest. Other then that: Good work!