Damn this game was good. I'd love to see you tackle more like this.
Other than some graphical glitches and other minor things. The only real problem the game had for me was the stereo audio. Enemies often sounded like they were from a completely different direction than they were.
The balancing could also be improved a bit. A bit hard perhaps since the player is so free to choose where they go, but for me, the game (on hard) went from somewhat hard to really easy around the mid point.