For some reason I suspect that the following is perhaps more difficult to translate into a 3D-game, but it is something I found very interesting and realistic in certain 2D-sidescroller (Megaman Zero, ZX and ZX Advent). Bear with me here.
In the prequels to those games games, whenever you hit a larger enemy or boss, whether you used a slashing weapon or other, they always took a single hit from it an went into an invincibility period that was signified by the character flashing. In later titles, the ones above, when I used a sword, I could slash across an enemy and I could hear multiple hits and I much to my surprise and pleasure
did do stacked damaged with my slashes, and I think only after that did bosses go into their invincibility period (but, I might be remembering that one incorrectly and maybe they didn't even have invincibility periods, anymore).
I want to get two things out of all that.
1. There should be enemies (not just bosses) that are
more susceptible to slashes and edged weapons than to blunt-force and vice-versa. For example, in case of armored kaijus, bladed weapons should be ineffective, either completely or they should be much less effective than, say, battle-hammers that could dent armor. In case of ranged weapons, incendiary, chemical (acid, thermite...etc.) rounds should be more effective than plain or any other projectiles. Cannot rightly say if energy-weapons would/should do more or less damage to armor. It's thermal-damage, in a way. Also, larger and stronger, low fire-rate cannons could burn a hole right through, at least, lighter armor, if not heavier plating. Punching, as blunt-damage, could only be useful against lighter armor, while heavier armor would need proper bludgeoning.
2. In case of bladed weapons on soft, fleshy targets, the bigger they are and the closer our weapon would hit and the wider the arc of the slash, the more damage the enemy should suffer, depending on just how close we could get with a sword, halberd..etc. We could have something like an e.g.:
reach stat for bladed weapons that would only allow for maximum damage within a certain distance. This is nothing new. But, I'd like to think the following might be. If we'd slash at an enemy close to the limit of our weapon's effective range, it could do only half or 3/4 of the damage, and if it's a big bugger than we'd only nick it with the tip of our swords, grazing it without much damage. But, if we slashed from an arm's reach away, well within range, then we'd be dragging our weapon deeper across the enemy and in a wider arc, doing more severe wounds that could cause bleeding effects and could even open up weak-spots on boss-type giants, so others could salt those wounds with incendiaries and toxic rounds that would be more effective fired directly into exposed flesh and innards.
Now, of course, I haven't a clue if it'd be possible to design such a...
damage-registering system. Or if it would be innovative in anyway. If some other game (of similar
scale), has such elements to it, then I sure don't know about it.
It would really create a difference, in purpose, between bladed and blunt weapons (haven't even included piercing damage, via e.g.: spears, but those type of weapons are not something I could see entering into such a game).
Bladed weapons would be most effective on softer, slower targets that we could get close to. While blunt-weapons would be invaluable for weakening armor and could easily crush enemies below a certain size.
These could
add stages to a larger boss-fight. First its armor would need to be weakened in certain parts, then blasted off. It'd be vulnerable in those spots, which
the AI should at least try to protect by orienting itself differently or by directing swipe attacks so they'd attempt to swat anyone who might try to get close and even try to shield those exposed parts on their bodies with appendages that they'd pull away when those would suffer enough damage. Hammer-wielding frames, supported by gun-fire (either from others or their secondary weapons) would reveal the flesh that would be vulnerable to attacks. Blade-wielding frames could, then, make them even more vulnerable and make the effectiveness of others even better by opening wounds. Attacks directed on joints could eventually sever limbs. Shooting at the head, once the armor(ed shell) had been stripped away, could achieve the same effect. Pelting the face and bashing the skull until it'd be full of gaping, gushing holes, by which time the creature would only need to be put out of its misery and it would fall to the ground, shaking the earth, as blood would pool around it from its mangled body.
Someone else suggested that damage suffered by enemies could be visually represented in different stages, but while my graphic description was only meant for effect, some minimal representation, at least, on the larger enemies would be neat. It doesn't even have to be detailed. Just blood-decals and some blackened spots for holes. Nothing major.
While I don't rea(listica)lly expect melee-weapon damage to be broken up into such distance-based effectiveness, just having bladed and blunt weapons differ in purpose and be suited for dealing with different kinds of layers of defense is something that shouldn't be too hard to include in the game, with minimal visual representation of weakened/exposed or critically wounded areas (blood decals on large enemies or just slightly altered meshes of affected spots, like how Chosen Obliterators needed plates of armor blasted off).