Enemies absolutely need to make noise when seeing you, firing and dying. It's too easy to be taking damage from an enemy across the room you can barely see and have no idea where it is. Also the fact that enemies don't get stunned when you shoot them means there is no way to avoid taking damage. The level design makes up for this with health packs, but it really doesn't feel good. Also the enemies could use a bit more variety. Just having "bot who stands there and shoots you" but sometimes with more health, doesn't really make for interesting encounters, throw in a melee enemy, or projectile based enemy.
Anyway. I don't mean to be too harsh, the actual level's flow well with pretty good enemy, weapon and ammo placement. Actually shooting feels ok (would be better if enemies gave you more feedback!) and the guns sound nice...