Pretty bare bones. The lack of recoil or ammo for the gun mean you can just spam click in an enemy's general direction and you'll still kill them in under a second. Having no warning sprite for when they're about to fire is also a bit unfair when they have hitscan weapons, and if you added a warning sprite you could increase their reaction time for a more difficult game. You can also clip through one barrel near the final area and reach the game over screen.
All in all it's decent for three days of work, and still had me hunting down the last few enemies in the maze.