A new challenger appears!
First NG audio submission, and it sounds good. 15 minute mix? Sir, you have a future that is considerably brighter than my LCD monitor on full brightness.
Its reminescent of Frank Klepacki's work in C&C Renegade, or any decent FPS (while Renegade was garbage, Klepacki's music is always good).
This song would mesh very well with almost any modern FPS game, and has a professional sound to it. I subtract one point only because songs that work well in a game are not always pleasant to listen to outside of the game.
Ignore that, however, its a sad necessity.
For what you made the song for, it is perfect. Flawless.
Keep up the groove bro; you've got it made.
The only thing I would suggest for improvement would be to up the guitar a wee bit. You did an excellent job by making the song gritty, but not too gritty (otherwise it makes the listener's muscles tense, which you would only want for a few parts of the game, and for no more than 4 minutes). Just a wee bit more 'WAAAGH!' would be nice, but only for a memoriable piece. Not every tune in a game can be memoriable, so meh.
Keep it up.