I like this! I think with a few tweaks it could become a good starting point for a full game!
- Enemy hitboxes felt a little large, which made avoiding damage a bit difficult at times paired with the limited visibility. (The visibility is not an issue to be clear!)
- It felt a bit rough moving up or down because of the way the camera follows the player. Perhaps adjusting it to follow the player a bit more strictly up or down would help a little?
- This one is more of a suggestion, but I know survival games tend to have system that make enemies more likely to drop certain items based on what you need most. If you have lower health, enemies are more likely to drop health packs, and ammo packs for lower ammo. This doesn't mean shower the player in these drops of course lol.
Good job :D