Ok! I tried out your game now. First i wondered why there was no music but then it started bip'n and bop'n and i was game on :)
I liked the small puzzles that came here and there and it was fun to shoot enemies and it was good that you had ENOUGH bullets/bullet clips.
The color palette was restricted but in a good way i think, you could see everything nicely and there were interesting enemies and i always felt an urge to kill every enemy! that is just the way i am programmed! 100% everything!
The animations were nice and the pause feature was also nice where the color palette changed.
I am however not a big fan of the controls since i suck at controlling movement with the arrow keys (that is just me). And also some sounds on hitting the enemies had been a plus, and maybe some sound when you shoot, maybe that was a priority thing tough. Then i wonder why the second room was slower.? Draw events that are taking the cpu to the roof perhaps?..
The game seemed to be longer than i thought, so maybe add some kind of checkpoint in the middle of the stage ?
Good job!