Hurray! Another person made a soundtrack to a 3d shooter!
Damn... THAT'S AWESOME! You have a very high quality atmosphere and texture to your compositions. The mix of rock, metal, classical instruments and synthesizers make the soundtrack cool!
Into Darkness (both versions) - set a good dynamic for everything that happens next
Old Friend - Brother... brother... brother...
Against the Dark - need I say anything? All groovy. Everything. As a culmination of this soundtrack - perfect
The only complaint I can point out, already mentioned by IndieKev, is the mastering.
P.S. Waiting for the game to come out)