Going in without reading anything :D
STAGE ONE - Interesting opening. So far, not what I'd normally expect from chiptunes. I like how you're constantly shifting the track in different directions in this one. It's in a constant state of flux. Cool glitching sounds everywhere. It's like we're tuning into this world.
STAGE TWO - From the music. I feel the enemies are getting more serious in this stage. Oh, love that thing you did with the hard panning. I really like how your soundtrack is constantly begging for attention by adding interesting little details, quirks and changes.
STAGE THREE - We're underground now, aren't we? Somehow the lowpassed opening sound makes me think we're somewhere far below street level and it's dark here. Second section makes me think there's some serious brawling going on. Really like the melody that kicks in approaching the end.
MISSION COMPLETE - From the soundtrack, I take it we won. However, now at the very end, some doubt kicks in. The very end sounded like it got a slightly unnerving twist.
Cool cover art too btw. It fits the soundtrack perfectly.
Great work!