Nice game.
I really enjoyed the graphics, really nice use of pixel limitations and clean finish. Some nice progression of difficulty also. Took me a while to get the hang of the controls as I was getting shoot direction mixed up with movement direction even in the more difficult rooms after playing for a while, but that's more of a reflection on my brain than on your game.
Maybe I missed it, but would have been nice to get life recover items/bonus items to help and difficulty increased?
Nice game.