Well this is what my entry ended up ad after about 12 hours:
Arrows or wasd to move
Mouse to shoot
1-4 to change weapon
M to mute the sounds
A new wave of enemies spawns every 10 seconds, It does tend to get a bit slow when there ends up being hundreds of them around. The 10 seconds here was just a last minute hack as I ran out of time to implement the intended link with the competition theme.
Try to survive as long as possible.
Edit: Uploaded an updated version with a few minor improvements.
Here is a timelapse video of the game's creation if anyone is interested.