I also agree with the comment below that this song would fit a cutscene really well. Personally I think it'd go really well in a movie as well. For me, it gives me the feeling that I'm back in the Arkham Asylum with the Joker up to his sinister plots, being hunted by criminals and having to hide in the shadows.
I don't know what this portal 2 mod is about, but the name " Repercussions" does give off an Arkham Asylum/ Bioshock sort of vibe. If this is what you're aiming for then you've hit the mark.
Frankly I find the quality of this to be astounding for a newgrounds piece and I'd include it in a standalone game , let alone a portal 2 mod. It must have really taken you a lot of time to make this. If I were you I'd put this in the game without any second thoughts. 5 stars. No question.
P. S. What VST did you use to get those sounds? They sound amazing.