The weapons feel punchy, movement has a nice momentum to it and you are fast but not to the degree that would make the main character hard to control.
I like the enemy designs, although it's a bit hard to tell apart the more dangerous variants sometimes. In Shadow Warrior they differentiate the generic ninja enemy by giving them different colors so brown ones carry an UZI while the orange ones fire missiles and such. However, I realize that might not be an option if you wish to keep the current style which is really charming.
The melee enemies reminded me of the fast melee guys from Post Void and they are almost as annoying. Good job.
Finally, the levels are not confusing and I like how the first one is a cinema like in Duke Nukem 3D.