I like the audio slowdown effect; that sounded really cool.
Starting the game, I died the first two times without even knowing what happened; if you don't commit running from the very first moment, you'll get killed without even knowing what happend; this is something you might want to change, especially for the first level to make sure people can get used to how the game works.
Some levels had no bullets spawn at all, but I can see where you were going with this. I loved the attempt at bullet time.