Shields should have three main features:
* Deflect - For smaller buckler shields, where a successful deflect will cause attacker to loose balance. If the weapon is heavy, this translates directly to the attackers stamina and speed to recover. But a missed deflect will still cause a world of pain.
* Bash - For the medium sized shields, where deflect and absorb is much lower. You may use it to bash harm right onto the enemy. A buckler would be too small to carry the amount of energy needed, and a big tower shield would be too heavy to use for this.
* Absorb - Your main worry is to simply hide behind the shield. It may restrict your movement speed, but it is truly an extension on your armor. A successful absorb will cause you little to no pain, but will degrade the shield. A good absorb will have greater effect on knockbacks, knockdowns, and even disarms, against the heavier weapons.
Weapons should also have different abilities:
* Deflect - Works precisely as a buckler shield, but less success rate. But also here, requires great skill to deflect bigger weapons, but rewarding when it does work.
* Parry / Trap - Used against lighter weapons. Try to parry a blow from a 50 kg Daedric Battle Axe with a puny sword - it smells like a fail. Trap is used instead for appropriate weapons, like certain daggers (i.e. japanese Sai), hand claws, and manriki chain. A good parry may knockback, knockdown, and disarm.
Oh, I could go on forever on what would be a "perfect system" for weapons. But this was about defense, so I'll leave it at that