I have to admit that I generally like really gritty heavy metal, and there's a really good chord progression in this piece that could grind really well, but there are some rather glaring problems with the composition. Please take this as constructive criticism, because I think this can sound way good with a little work...
1. The dynamic range is too large - At 50% volume, I couldn't hear any sound until about half way through, then for the last 50 seconds, it sounded like it was hard-clipping. I know the intent was a gradual fade effect, but the spread is too much. You can achieve the same effect with a -12db to -3db range at full volume, then if I set my master at 50% I should still be able to feel it.
2. The rhythm timing is off - or, more to the point, it seems arrythmic. I don't really know if this was your intent, but setting the frame of the piece within a solid time signature can really accentuate the points when you want to "break away" in syncopation.
3. Try variations on your primary chord progression - it can add the gritty flavor I think you're trying to achieve with enveloping dynamics through shifts in harmony.
Anyway, just a couple of suggestions I think could make this piece shine. Take them with a grain of monosodium glutamate. 2/5