Interesting and ambitious to transpose the design of the 2D roguelike into a 3D world. I like the tricks you've used to keep the spirit of the roguelike by having blind corners to trigger random encounters, and limited ammo requiring careful management of resources. A contemporary theme with - as the title says, guns and zombies - feels a little more fresh and interesting than the millionth dungeon crawl with swords and generic monsters.
For constructive feedback, there's a few janks to iron out that might make things a little smoother to play. Controls are precise, but as the other commenter has mentioned, a pivot/swing to allow the player sprite to turn towards the mouse aim would help. Bullet control is paramount, but if you run out, there's not a lot you can do but twiddle your thumbs until you die. Maybe a weaker melee could add a bit of a last-ditch option?