Critical Hits

Gary Was Correct
In 1975, a year after publication of the White Box, TSR published Empire of the Petal Throne which included the rule that a "natural twenty" score on the to-hit die is a critical hit and deals double damage. This was a time when the new hobby was developing rapidly and the idea of a critical hit was making it's appearance in various "house rule" innovations to White Box, such was described, alongside numerous other rule innovations, in several of the amateur publications of the day. Published games starting in the late 1970's and right up to the present have frequently included a critical hit mechanic. The Arduin Grimoire (1977) includes a rather detailed critical hit table, which can result in instant death. Chivalry and Sorcery (1977) and Runequest (1978) soon followed suit with mechanics for the "critical hit".
The only mention of critical hits in the White Box is in volume 3, Underworld & Wilderness Adventures, when discussing aerial combat a Critical Hit table is provided. This critical hit works in conjunction with a hit location table (Blackmoor would include a hit location table for land combat). The Critical Hit table lists percentages of a critical hit occurring by location and ranges from 25% if the rider is hit on down to nil for a tail hit. The effect of a critical hit depends on the location and if it's the rider, the beast withdraws from combat. Other critical hits can result in loss of speed, dive and land or crash - dead in air!
E. Gary Gygax wrote in Dragon #16 (July 1978), and in other places (including the DMG), that he disapproved of the critical hit idea. In the article he writes that the inclusion of critical hits and double damage does violence to the game and can possibly result in ruin, especially in the case of the instant death of characters or monsters which unbalances the game and makes it difficult for the player to use their judgement in play, i.e. to predict how dangerous certain monsters are. When even a lowly kobold can lop one's head off with a lucky referee roll of the die, how does one know when to run away? Every encounter becomes much more of a gamble. Also, low-level PCs may take ill-considered risks on the off-chance of rolling a natural twenty and slaying a huge dragon. If that happens the resulting treasure hoard may be described a "Monty Haul".
In the same article Mr. Gygax challenges the trend for players to want more realism in their fantasy game. He points to the inherent contradiction between what is real and fantasy (including "magic") as well as the fact that no "game" can replicate reality. The desire for a more realistic feel, for verisimilitude, continues to be a factor in role-playing games to this day. Many popular game systems start out as an effort to design a more realistic game and market the resulting product as such. I admit my own occasional the desire for more realism or at least verisimilitude, has prompted many of my own gaming hobby decisions. There is something visceral and satisfying about being told your mace connects with the baddie's lower leg bruising flesh and crushing bone resulting in a crippling wound and the baddie drops prone before you. But I have also found there is no reason a referee cannot use such colorful language to describe a simple White Box hit that does an impressive number of damage points. Verisimilitude, rather than realism, is the actual goal here.
Is this a point on which there is room for a difference of opinion? My answer is a resounding "yes, of course". Mr. Gygax is making a point and I think a good one, however. The ability to judge damage dealt and taken is key to many games including White Box. Each Hit Point is determined with a roll of 1-6. Each weapon hit does 1-6 points of damage. It almost reduces the point system to a creature who has four hit die can take four hits, one-for-one. Rolling the die adds some degree of unpredictability, but double damage, maximum damage and especially instant death crits can significantly alter expected outcomes. Is White Box the delicately balanced, finely tuned Swiss watch Mr. Gygax seems to present it as? "Not hardly", I would say, but I do like the game better without critical hits.