So to make this amazing game even better, I noticed you can add your own custom combat music. 
 
From in game main menu, go to options and hit audio. All the way at the bottom is the option for custom combat music. From there click the add button to browse your way to your music library. 
 
Imagine the last sequence when you're running your ass off, to the Super Metroid escape theme....
 
So yeah I recommend you go check it out. 
 
EDIT: "Life is Beautiful" from Deadly Premonition fame fits hilariously well too! 

That's pretty cool, but how do you use it? I added a couple songs but it doesn't seem to do anything.

I think its only during certain parts. Like whenever the music changes. The first one that comes to mind would be the slo mo fight on the elevator.  
 
This is only a guess though.

I think it's a really cool idea. Killing aliens to "Titus Adronicus Forever" by Titus Adronicus, and running at the end to "March Of The Pigs" by Nine Inch Nails made the experience ever better.

" @ThePwnee:   It'll play during the stand off sequences.  With multiple songs, I think it cycles through the list, maybe random. Not quite sure yet. "

Amon Amarth helps greatly

I recommend Blotted Science. Instrumental-only songs are best.