Sure, here's an example of a simplified 3D shooting game implemented in a single HTML file using JavaScript:
This game features a simple 3D perspective, where the player is represented by a green rectangle, enemies are represented by red rectangles, and bullets are represented by white rectangles. The player can shoot bullets at enemies by clicking on the canvas. The score is displayed in the top left corner.
Note that this is a basic example and can be expanded upon to include more complex gameplay elements, graphics, and sound effects.