Length/m - the longer the weapon, the higher the penalty to fighting in a restricted environment (e.g. a tunnel). There should also be a penalty for the character in combat who has the shorter weapon, with the penalty proportional to the difference between the two
Weight/kg - the heavier the weapon, the more strength needed to wield it, and the higher penalties if the strength is not sufficient. If an energy model is used, wielding a heavier weapon takes more energy.
Sharpness/penetrating ability (thrusting attack) - a spear would have a high penetrating ability for a thrusting attack, whilst an axe would have a low penetrating ability for a thrusting attack (unless it has a spike in addition to the axe blade)
Sharpness/penetrating ability (slashing attack) - an axe would have a high penetrating ability for a slashing attack, whilst a spear would have a low penetrating ability for a slashing attack (unless it has a blade more like a halberd)
Types
Shaft (e.g. sword, spear, etc)
Shaft-flex (e.g. flail)
Shaft-flex-shaft (e.g. nun-chaku)
The shaft may be metal, wood, bone or stone; the flex may be rope or chain.
It should be such that different weapons would be suited to different missions, so the characters can chose particular weapons for a mission based on the known characteristics of the mission, and the skill of the character.