UPDATE:
Wow, that's actually what you went for??
In that case, you did an excellent job. :)
Now, in theory, you could try to raise the volume via normalization and/or messing around with compression/limiting plugins, but I'm not sure this piece really needs it.
I can't think of anything that would definitively improve this piece. Re-rated to 5 stars!
Original 4 Star Review:
"The tension of this piece to me really feels like something out of either a horror game or a post-apocalyptic NYC underground subway station; the vibe in this piece is quite eerie.
I'm not sure if that's what you are going for, but the direction you went is interesting. Please feel free to correct me if you think I'm wrong.
More info about how I review music here: https://codefreq.newgrounds.com/news/post/1089806"