Interesting, I enjoy the beginning, the loopy sounds after and the electronic sounds around 4:00 are a bit loud for me, but I have crappy speakers here so it's hard to say. I think the song would benefit a lot from vocals, have you thought of adding them? Maybe just to some parts..
All in all it's good, very atmospheric with the main theme kinda going on and on. I guess this would fit a video or a game very nicely.