As opposed to all the other rolls that were hits but not crits? Those were sloppy and weak? Even a non-crit that deals 3 damage when the fighter is at 2 hp is apparently strong enough to kill a fighter.
Damage and HP are game score devices translating danger to players, not a scale of medical severity for characters.
The biggest problem with hit points (ie - "points for tracking hits") is that people naturally infer that the biggest damage roll against a character = biggest wound. I'm not sure there's any fixing that inclination to conflate player-reality and character-reality.
The 20-point hit that brought you to 2 HP over bloodied is more game damage. The 3-point hit that brought you below bloodied is the one that actually busted you open. It did more
physical damage to the character than the attack that did more Hit Points in damage - because Hit Points represent the ability to avoid or mitigate physical damage. That's the difference between the game-world reality of the characters and the game-system reality of the players. I guess the confusion comes from the word "damage," really.
Nah, rolling a natural 20 should be a WOO-HOO moment, not a moment where the result is: "Your enemy is badly scratched by your amazing attack."
The problem is the Crit cuts both ways. Have you ever seen the d30 critical hits table from the old Armoury book that went with the d30? It looks awesome - until you realize that monsters are disposable so the enemy team can just ignore having their teeth bashed out and losing 1d6 Charisma permanently, while the players lack that luxury with their characters.
I'm very much in favor of critical hits having remarkable impact - some sort of lasting damage (maybe just for the length of the encounter, since that hits PCs and Enemies equally) beyond HP would be nice. Compromising their defenses or attacks for the encounter by destroying someone's shield, shattering their armored carapace, or impaling the shoulder on their sword arm all work quite nicely.
But, as you say, that's something fixed by a module - and rightly so! That's a layer of complexity added onto the game.
Even if they are just damage and it doesn't reduce a monster to the bloodied / injured state the dramatic narrative doesn't need to be spiked by talk of "scratches" and the like. A barely parried blow that drive an opponent to its knees or leaves them reeling and gasping for breath as death begins to circle them like a vulture works pretty well too.
Also, there's no rule requiring that monsters with a 1-encounter lifespan follow the same HP narrative path that PCs do. If that 20-foot tall spider takes a crit, feel free to have one of her 8 legs come off - no module or rules adjustment necessary.
- Marty Lund