So, I liked the music a lot, and the credits were quite funny. The atmosphere was cool and I liked the lighting effects.
What I didn't like was the level design. It started out ok, but once you get into the MASSIVE EMPTY HALLWAYS.. it's just is really boring.
Also, I think not allowing the player to move and shoot at the same time takes the fun out of the combat. I also think the combat would be more fun if, in addition to move/shoot at the same time, the enemy bullets were much faster but less of them. Also, the pistol and shotgun seem pretty useless after you get the machine gun.
And on the art, if you use a pixel art style, you need to make everything a consistent pixel size. It looks like everything has been scaled to a different size, so you have small pixels on the character, but giant pixels on the shockwave effect and the UI elements.
I hope you learned a lot and I hope your next game will be great!
OH! I can't access your Game Design Document. Might wanna fix that.