3.0 made some ... interesting ... decisions on crits. The tagline of 3.0 was "Back to the dungeon". And in a dungeoncrawler the same applies to crits as did in oD&D. They take away tension. They also mean that a normal orc who rolls a natural 20 to hit (and confirms) can threaten PCs well above the orc's level while being strawberry jam if the PCs hit first. Again, this throws planning into the lap of the dice and makes building specific tension harder. Not good for a dungeon crawler. Also sudden death out of nowhere works much better when you can roll up a character in only a couple of minutes than when you have a massive list of skills.
3.5 made the decision not to change crits. With the emergent eggshells-wielding-sledgehammers of 3.0 Save-or-Suck spellcasting this was almost the right decision. Fast kills and one shots fitted with the rest of the game. The part of critical hits they should have changed is simple - the confirmation roll is a step that only ever disappoints people and should have been eliminated.
4e had wimpy crits. Which mean you can plan for them thus not undermining the tactical game so much. But not giving the emotional high to the people who wanted it. It also sufferered a second problem: rolling dice is fun - there were people who'd prefer not to roll crits in 4e and that is something that should never happen. The 4e critical rules therefore are ... useless. (Oddly enough 4e with Dark Sun had the best critical failure rules I've seen in any system).
5e crits are good. Not especially powerful (a good thing). But noticeable - especially to anyone with the kinaesthetic sensibilities to like an extra dice in their hand. They fit with the rest of the game, they feel good without unbalancing things - and they don't undermine the strategic risk management side. They could be seamlessly transferred to 4e and improve the game slightly. They make a dent in the risk management, but not an extreme one - but they provide the acknowledgement and emotional high the people who want crits are seeking. As good a compromise as I've seen for a game that's trying to do most things rather than any one thing spectacularly well.
Back to the OP....CRITICAL HIT CHARTS
My first use of a Crit Chart came from Dragon Magazine. It was a percentile chart that one of us typed up. Good gods, it was deadly. "Critical Hit Friend" came up more often than we wanted. And, as I got older, I realized that the chart was no good for the game. The PCs were exposed to its effects a million times more often than NPCs. One PC may fight seven goblins. That's 7-to-1, right there, against the PCs. The longer you play, the higher the probability that the PCs will get maimed if not killed. We ended up with all sorts of injuries. Eyes missing. Missing limbs. Missing fingers or ears were common.
It was just a big negative for the players. So, we dropped it.
We still laugh, to this day, how Sturm Brightblade died when playing the first DragonLance adventure, DL1, under the original AD&D rules, back in the day. Riverwind, standing next to him on a ledge in the dungeon at the climax of the adventure, pulled a javelin of lightning out of his quiver on his back. The player rolled a natural 1 on his attack. The Crit Hit chart roll was 00 or some other awful number close to that. The line said, "Critical Hit - Friend". It was Sturm, standing behind him on the ledge.
So, what happened was, the dragon came flying up into the upper parts of the lair. Riverwind braced himself, then drew his javelin, cocked it back a little too far and stuck Sturm in the chest. Bbbzzzzzt! Sturm was stabbed and fried and fell to his death.
Poor Sturm.
Yeah, it wasn't long after that when we retired the Critical Hit Chart.
Afterward...NO CHART, OR SIMPLE RULE, OR MORE SENSE
For years afterward, we used nothing. Or, we used this simple method that seemed to be fair:
Roll natural 20, it's double damage. Roll natural 1, your enemy gets a free, extra attack on you. This was all pre-3E.
I have seen some Crit Hit charts that work well. There is one designed for Mongoose's Conan RPG (yet, I don't use it). Whenever a Crit happens, you throw for extra damage as you do normally with the 3.5E d20 System. But, you also roll on a chart. The chart is skewed so that, more often than not, the extra injury effect is just bothersome and lasts for a limited time. Effects were like: Helm rung, hearing at -50% for 1 hour, or Knee Bashed, movement halved and no running for 1d6 hours.
That type of chart is much more playable. Rolling on the chart is a Saving Roll instead of a random roll, and with the chart being skewed, you really have to brick the save in order to get a result where your character dies or is permanently maimed. If a chart like this is written well, it can be used without the PCs taking the brunt of the awful damage, coming out of the game maimed.
But, a lot of thought must be put into creating such a chart so that it is balanced.
My favorite.....GUSTUD!
I created a rule for my d20 Conan game that my players really like. It's a type of Critical Hit chart, but it is different from those discussed above. It only applies to melee (not ranged attacks). And, the standard d20 rules are still used (natural 20 still causes a Critical Threat that needs to be resolved).
On a Melee Attack Throw, when a Natural One is rolled, the GUSTUD rule is triggered.
Roll 1d6
1. Grapple
2. Unarmed Attack
3. Sunder Attack
4. Trip
5. Unarmed Attack
6. Disarm
Typically, an Attack of Opportunity is given to the defender when most of these special attacks are attempted. But, when given to a foe because of a roll of a natural 1, the AoO is not allowed. This means that the natural 1 triggers a special attack by the character's foe.
Now, the foe does not have to take advantage of the special attack. And, why wouldn't he attempt the special attack? Well, because most of the special attacks give the target a recourse action if the special attack is failed. For example, if Able attempts a Trip on Berkus and fails, then Berkus gets to try to trip Able in return.
Secondly, a character may not want to take the combat in that direction indicated by the special attack. For example, if a Grapple can be attempted, a character may not want to take advantage of that attack because he may not be a good match for the grapple attempt, or he may not want to take the combat into a wrestling match at this time.
--
So, there are times when the Natural 1 is rolled but the foe doesn't take advantage of the opportunity given him.
-- And, there are times when the Natural 1 is rolled when the foe does attempt the special attack but fails. The Natural 1 turns out being a boon for the character who rolled it (instead of a penalty).
-- And, there are times when the Natural 1 turns out to be a fumble for the character who rolled it. It just depends on how the special attack plays out.
In our combats, we've found the GUSTUD rule really livens combat, making it exciting. You never know what's going to happen.
And, our fights end up looking more like this:
COOL SCENE FROM THE MOVIE "CENTURION"
