666...
4x4x4x4x4=1024
3x3x3x3x3x3=729
so... bullet speed, bullet path, rate of fire, triggering mechanism... damage effect... area of effect...
Bullet speed= instant, fast, slow.
Path = arc, flat, seeking.
Rate = effectively constant, precision.
Trigger = immediate, delayed(charge up for a time before shooting), option to delay(can be charged for more power per shot, presumably for ammunition conservation).
Damage effect= none, effectively permanent(like, it only goes away after, like, two minutes without being hit.) speed reduction, damage over time over an area, temporary(like, if resets after five seconds of not being hit) damage vulnerability... Increased reward(If there is no reward for shooting things, then maybe grant some form of self-recovery proportional to damage-dealt?).
area effect = line, penetrating line, wedge, explosion on impact, explosion at fixed range.
3*3*2*4*4*5=1440
I think that these variations would be distinct enough to each have their own feel, although some weapons would be less desireable. Even with significantly greater damage as compensation, a slow projectile with no seeking or splash would be painful to use against anything but the easiest of targets.
Graphics would be a pain, you could have symbolic-based weapon, using spiritual energy as ammunition, which would probably regenerate, but be drained by various environmental effects and be used as a shield against some threats so ammunition would be perpetual but require management. That way you could have a few generic graphical objects, such as a necklace, pendant on a chain, rings, wands, belts... And have a bunch of skins with various random geometric forms and assorted bits of obscure heraldry. Because it is all based upon symbolism and is acting more as a focus for other forces than an actual mechanism, it doesn't need to look as though it actually works, which saves on having hundreds of remotely-convincing AND unique gun images, you just need something where a simple palette-swap will keep the peripheries from being obviously identical and with a distinct pattern prominently displayed somewhere to keep it unique where the player is focusing. Probably split the graphic along the properties, the symbol is always based upon its effects when it hits something and the form is always based upon how it comes to be hitting something. Instant laser-beams always come from wands, homing laser-beams always come from two-handed wands with spiky bases, stuff that slows the victim down always have a symbol of an eye and if it explodes then there are teeth around the edge or the object looks rusty or something...