Of course, we handled it differently over the years. There were hit location tables, confirming crits, secondary tables with more abstract things than direct hit locations (Bleeder!), and the ubiquitous double damage. It was the double damage we generally used most often. It was faster, less fiddly, and quite a visceral experience to slap some jackass with 28 points of damage.
The enemy could score crits on the players, too, and there was always the dreaded fumble. This usually was simply fall or drop your weapon. Either way, you basically missed your next turn.
I'm not such a fan of critical hits these days, and I'll tell you why.
- D&D combat models results. It's roots are in a wargame, and a wargame is concerned with who wins, not how. Any sort of critical hit system intrudes on the model.
- Combat is conducted with a d20. It is based on linear probability, which means the stable boy and the war hero will crit 5% of the time. Now, I know that confirming your crit mitigates this, but who wants to fiddle with another roll? And have you ever seen a player in a desperate situation that failed to confirm? It isn't pretty.
- The roll to-hit is simply that, a roll to-hit. The only possible rationale for basing a critical hit from that would be to assume that a high roll (a 20) could indicate a hit to a more vital spot.
- To me, it really should be the damage roll that indicates a crit. I have no system for this because I do not desire one. I am merely speaking hypothetically. Exploding damage dice or something. I just think that it is silly to roll a 20, double the damage, roll like a 2, and end up with a "critical hit" doing maybe 6 points. A damage roll that indicates max damage is more critical than that.
I am an old-schooler when it comes to weapon damage. I love the idea of all weapons doing d6. So, and this is completely off-the-cuff as I type this, I think if was going to introduce crits, I would just allow an additional d6. Maybe. I don't know. I just know we are trying to model outcomes and introducing subsystems like critical hits into the model engine are doomed to either fail or disrupt the engine.