Well that was a nice round with quadraxas and schokokeks.
My personal record: 55656 points

Here some ideas:
- give the creates gravity (was already mentioned)
- balance the enemies and create classes (examples below)
- - fast enemy, making little damage, having not many healthpoints
- - normal enemy, making average damage and having average healthpoints
- - slow strong enemy, making lots of damage, having lots healthpoints

I know there is already some balancing and some enemies are faster than others but maybe you could work on that a little?

- Define hit-zones, maybe even some which are not always very vulnerable (for very strong enemies e.g.)

- enable changing weapons while reloading (but this could also be a tool to make the game more challenging)

Well all in all I can say this is already a very good game, making lots of fun playing with others. If you are on your own its not all that exciting though (my opinion).
This kind of game could be transferred into lots of different settings:
- futuristic: think of star ship troopers, alien closing in and you laying heavy fire on them (pistol, shotgun, mg, sniper, atom grenade)
- fantasy: more a hack&slay setting with mediaeval weapons (dagger, sword, bow&arrows, crossbow)

- player classes:
- - soldier (different kind of weapons and upgrades)
- - medic (smaller amount of different weapons, but can heal himself and people)
- - ...

Keep it up! This could turn into a very good 3DGS multiplayer game!