The only reason for them to exist at all is to satisfy the intuition that you should get something special for a natural 20.
Which is funny since hitting or missing is otherwise binary. IIRC it was in a Dragon or Dungeon magazine or something when the concept of the critical hit was offered since in 1E it wasn't part of the game.
Personally, I hate critical hits. They have long been either double damage or double dice. Then, because people got upset when they rolled 1's, people started making it max damage
and a roll. We've long used simply max damage (no rolling) if you want, or double dice. I prefer just max damage, if anything.
But, I'd rather not have them. It is one thing if you want a nat 20 to always succeed and a nat 1 to always fail for attacks, ability checks, and/or saves. But critical hits also open up people to critical fumbles, critical saves and ability checks, etc.
Personally, that seems like a minor enough addition to the math load that players would hardly notice the extra effort.
Granted, it isn't
a lot, but IMO it is just an extra step, which makes combat take even longer because you have to do the mental work on every attack (as minimal as it might be for many people).
Now, I don't think it is a bad idea really, just not for our group. On the upside of things, more critical hits means more damage, which
could in some ways make combat a bit quicker. But you realize this really favors PCs IME. A PC can get a better AC than most of the foes they go up against, which means PCs will more likely roll criticals than monsters against them.
The nat 20 is fair because it gives even chances to work both ways.
Or an argument to make crits do something more interesting than just more damage, which I'm on board for.
We added Skewer, Stun, and Wound properties to piercing, bludgeoning, and slashing attacks. If you roll a 20, the target has to make a save or suffer effects:
Skewer: DEX save. DC = 8 + attack modifier. Failure means target is skewered on weapon and has speed 0 until the end of its next turn.
Stun: STR save. DC = 8 + attack modifier. Failure means target is stunned until the start of its next turn.
Wound: CON save. DC = 8 + attack modifier. Failure means the target is bleeding and automatically takes the same damage again at the start of its next turn.
We've thought about options as well for knocking prone, frightening, etc. A lot of the conditions could work well IMO for critical hit riders instead of just damage all the time.