I've rated the game, and I'm sorry but I'm a bit exhausted from giving a lot of in-depth feedback for a bunch of games, so here's the gist of my feedback for you;
- Give more game feedback to the player: The player should be able to see and hear every time they hit an enemy and when they get hit by an enemy
- Fix the health bar, please.
- Consider adding some sort of limitations and incentives for the game. Right now the game is just "hold down left click and aim at the bad guys". Maybe consider limiting the number of bullets in each gun, and force the player to physically pick up new guns when they run out of ammo to add more skill and thought to the game.
- Maybe try revising the colour palette for the game. Unless you can afford to draw custom sprites for everything, just stick with coloured boxes for everything, giving everything very distinct colours. SuperHot is a great example of this, with only 3 colours for the whole game, yet everything stands out and these colours do a great job of communicating what's an enemy, what can be interacted with, and what can't be interacted with.
- Increase the player's movement speed to make the game feel more responsive. It doesn't feel like it when you code it, but just changing the speed of the player makes a huge difference.