There's plenty of pen and paper systems that would be perfect for a computer game adaptation, but which haven't been turned into a CRPG yet.
Several complex systems from the 80s come to my mind, using a hex grid with positioning (bonus for flanking, attacking from behind, etc), locational damage, wounds instead of HP, etc etc. Those require a lot of recordkeeping in pen and paper and make combat a drawn out affair (which is why they tend to be less popular than D&D) but since a CRPG has the computer take care of all the calculations and recordkeeping, these systems are perfect for adaptation.
Yet the systems that tend to be adapted are usually relatively simple in their rules. Not even GURPS has been turned into a CRPG yet, and that's on the less complex end of the more involved systems.
This is something that has bothered me since I started to play TTRPGs in my teens. I understand why DnD has such simple combat rules, but when cRPGs eliminate the tedium that was the innate restriction the weapon/armor dynameics cease to make any sense. Most of the weapon variety is, aside from a few relatively unimpactful instances, just flavor and serves no meaningful purpose - it's mostly a guessing game on your first playthrough which weapon category will be most powerfully itemized in the game and then when you know what to expect you choose the same weapon every time. E.g. you would probably pick Bastard Swords in BG2 (to dual weild with Belm) to go Foebane +3 -> Jhor the Bleeder -> Foebane +5 (Jhor and Foebane +5 are stupidly overpowered) or Flails to use FoA (+3 -> +5) throughout the game. Or maybe you think some specific weapon is cool, so you use that one and it's not necessarily much worse than the alternative and it works just about as well in every single encounter no matter the opponent - so the distinction is ultimately meaningless. Weapons don't have strengths and weaknesses, they are just better/worse across the board and maybe some cool ability that usually doesn't make much sense to begin with.
The weapons are based on IRL counterparts which were developed for very specific circumstances, but these dynamics are not reflected in the game at all. Full plate mail would make you virtually invulnerable to any one-handed cutting weapon and thrusting weapons require the equivalent of a critical hit to do anything at all, but a halberd (always insanely underpowered in every DnD edition) would be a serious threat. At least in 2E there were some type-sprecific modifiers (though full plate was still not nearly good enough), but in 3E some dumbfuck with two Kukris can bring down a knight with ease. When these dynamics don't exist, why do things like halberds exist at all? If we compare halberds to greatswords; they have the same proficiency requirement, the same crit threat (halberds are 20/x3, while GS are 19-20/x2), greatswords have significantly better base damage 2d6 vs 1d10 and the only outright benefit of halberds is that they can deal piercing damage which AFAIK NEVER comes into play in NWN since armors don't have specific AC modifiers and IIRC there are no enemies that are vulnerable to piercing but resistant to slashing. There is NO mechanical reason to use a halberd over a greatsword. Compare to IRL where a skilled warrior had to be a master of many weapons since each one had significant drawbacks in many situations.
I've been toying around with an idea of creating an NWN module with totally revamped combat mechanics along these lines:
- Slashing damage would be by far the most powerful, but most armors would offer significant resistances (both in terms of AC and outright damage reduction). For example: a full plate mail would be impervious to slashing damage, have exceedingly high AC against piercing (but no damage reduction) while having low AC against force damage, but with some damage reduction. This also requires that full plate mail is exceedingly expensive and needs to be tailor made for a person - making it rare and undroppable among NPCs and an endgame item for the PC.
- Every weapon would deal some amount of "blunt" damage (force damage). Blunt weapons deal purely force damage, halberds and axes deal more than swords etc.
- Straight swords would akin to halberds be able to deal piercing damage as well as slashing (reflecting the differences between curved and straight swords and why the two types exist to begin with).
- Conversely, curved swords would deal more slashing damage and be more powerful against unarmored or lightly armored opponents (which is why they were much more popular in regions where heavy armor was rare, like the Orient and East Asia).
- HP only minimally increases throughout the game, everyone is 1HD (levels are abolished for a pure use-based system) only boosting your constitution can increase it. This ensures that the low-early midlevel danger is ever present through the game and maintains some realism.
I think the dynamics of such a system could be interesting. Groups would be much more powerful unless someone has heavy armor (like IRL), shields would be an absolute necessity unless you have heavy armor. Two handed weapons (or blunt + shield if you don't have the armor to back up a two hander) are a must against heavy armor whereas cutting weapons are just as dangerous against a lesser armored opponent (if not more since they are, or rather should be, faster). Since one good hit is a death sentence, initiative is much more important. It's no longer a DPS race, but a race to get the killshot.
I'm programming a combat simulator to see how the system would play out and how to balance it before I dive into implementation, so hopefully it's not just ideas that seem to make sense in my head (and not just an RNG-based orgy of savescumming). I've been wanting to play an RPG system with low HP dynamics since I was 14 and me and my older brother made an attempt at a homebrew that was rejected by the rest of our D&D* group.
*Drakar och Demoner, Swedish TTRPG that at least had separate HP pools and the way we played leveling was extremely slow, don't think anyone in our group ever went above level 3.
