Critical hits and their place in D&D have been a matter of contention and common house-rule and core rules over the editions. Many an old timer rejects critical hits, forgetting they were with the game from the origin.
Does the game really need them, no of course not, if you don't want them don't use them. I'm going to give a brief overview and criticism of early critical hit systems.
House Rules from Unknown Times (that may or may not have gotten into the rulebooks later)
The Ancient Critical Hit on a 20 houserule:
On a to hit die roll of 20 the blow scores double damage.
Players love this rule until the monsters that dish a lot of damage also deal out critical hits. Well okay some players still love getting characters bitten in half. The bummer factor with this commonly applied house rule is when you roll a 1...woo hoo 1x2 is 2 a massive 2 potions of damage, not so exciting or all that critical a wound.
The keep on hitting critical rule:
On a hit roll of 20 you get to make another attack. Apply damage for successful attacks. Kinda cool, you aren't likely to get stuck with a massive critical hit of 2 points of damage but you also might not get any extra damage at all. It also slows down play with more dice rolling but there is the exciting chance of more and more hits and a non-hardass DM might allow the extra attack against another target if the first would likely be finished off by a single blow.
TSR Critical hits
In the olden days the critical hit was included in D&D from the get go and in supplements and in a similar game.
Arial Combat Criticals from Book 3 of the original rules.
The originasl edition of D&D had a subsystem for arial combat in book 3 and hits on flying creatures could score critical hits in arial combat.
Depending on angle of attack one had different odds of striking a flying target in the head, wing, body, tail or rider .
Once the location hit was determined it was then possible to determine if a target was reduced to 1/2 speed, forced to land, forced to withdraw or crashed.
This was clearly some sort of carry-over from WW-I flying games and certainly meant to play out combat between such combatants as roc riders and dragon riders. This method however does have potential to carry over into the rest of the generally abstract nature of the game but it curiously was restricted to flying monsters.
Hit Location and Blackmoor
In the second official D&D supplement a detailed hit location system was presented and while it wasn't explicitly a critical hit system it sure functioned like one by allowing folks to deal and suffer even more random death upon foes.
Combatants could each be struck in different locations and each location had it's own HP score based on type of creature and full HP. Your head had 15% of total hp, the chest 80%, the arms 20% each and so on.
You were killed when total damage suffered to various body parts reached 100% of the normal total or when ones head or chest was destroyed by taking it locations total in damage. Limb damage caused a crippling loss of dexterity.
Now all that was sort of realistic but it was also a bummer as most characters and monsters in D&D lacked HP totals to make it much of a point to calculate the results. Almost all 1st level characters are instantly killed on a head hit (as 15% of 6 is 1). 50% of all head blows would end up killing any foe with less then 30 total HP.
Brutal indeed but D&D characters really don't have enough hp to make it fun paperwork it was really a "bang you are dead" critical hit system.
I did use this system with a GW campaign and it worked great there, but the average character in that game starts with 33 hp.
EPT Double Damage and Instant Death
In the Empire of The Petal Throne game which was described as some in the olden days as being vanilla D&D (vanilla? really more like ginger and rose water if you ask me) was essentially a D&D rules variant published by TSR and one could find a critical hit rule within that may have spawned one of the common house-rules mentioned above.
In EPT any hit roll of 20 does double damage and entitles the attacker to make another roll to try for an instant kill if a second roll comes up 19 or 20.
Pretty fierce and random along with the excitement of 2 pt critical hits. I'm not surprised the instant death variant wasn't a popular variant in many a house-ruled campaign.
So there you go an exploration of early critical hit systems in D&D. Critical hits add excitement and an increased random chance of death of beloved PC's and Mary Sue NPCs with varying degrees of playability and annoyance. I've used all of them in my games but one saw very limited use and I know I'm going to explore that one for future use in my games and in a future post.