Nice little game. What could improve it a lot:

- reloading gun

- automatically loading the next level

- shorter cooldown between shooting a bullet

- smaller mouse sensitivity or a slider to set it

The direction is good, keep it up and you'll improve fast!

I think you were trying to go in the direction of Doom or Quake, which is definitely retro. Maybe try starting the next level automatically after the player finishes the first one. Apart from that, it's a simple and nice game.

Fun